A Regal River Runs Dry

Rising from the snow-capped San Juan Range of Colorado’s Rocky Mountains, the Rio Grande River descends through New Mexico, nips the western tip of Texas, then snakes eastward, marking the Mexico–US border for hundreds of miles before finally emptying into the Gulf of Mexico. In the sixteenth century, Spanish explorers christened the Rio Grande “the Fierce River of the North” (El Rio Bravo del Norte) out of respect for the turbulent cataracts in its upper reaches. These days, however, the once-regal river has been dethroned by a confluence of forces. Explosive population growth, increasing demand for irrigation and industrial uses, a decades-long “mega-drought,” and rising temperatures attributed to climate change have conspired to dramatically diminish the river’s flow. In June 2021, observers watched with horror as New Mexico’s Elephant Butte Reservoir, which had brimmed over during the 1980s and 1990s, dropped to a paltry 5 percent of its full capacity. Other reservoirs that feed the Rio Grande have experienced similar distress due to rising temperatures and growing demand, forcing regulators in Mexico and the United States to adopt extreme rationing policies that restrict the lower basin to about 2 percent of its historic annual flow. Residents of Albuquerque, El Paso, and Ciudad Juarez have seen the Rio Grande run dry for longer periods each year, its mirrored surface replaced with a parched sandbar.Footnote ¹

Dwindling fresh water threatens vital interests on both sides of the Mexico–US border. Over six million people rely on the Rio Grande and its tributaries for agriculture, industry, and municipal uses, and population centers in the region continue to expand. In the past, farmers in southern New Mexico and El Paso County could count on forty inches of water to irrigate their onions, corn, and green peppers; by 2021, some received as little as four inches. Across the border, Mexican pecan growers have complained likewise that water rationing is imperiling their groves.Footnote ² Less water to go around means fewer acres of arable farmland, shorter growing seasons, and mounting pressure to transition to more drought-resistant (but generally less lucrative) crops – all of which equates to fewer jobs and diminishing profits. Meanwhile, ecologists have expressed concern that hydroelectric dams are imperiling the basin’s flora and fauna. Hundreds of native plants and animals have been decimated by the region’s changing ecology, including the endangered silvery minnow and cottonwood trees that have evolved to rely on the basin’s natural hydrological cycle.Footnote ³ To make matters worse, scientists predict that current drought conditions are likely to get worse over time, as climate change continues to dry out the Rio Grande basin while inundating other regions with floods and hurricanes.Footnote ⁴ As the fresh water crisis in the Rio Grande Basin has dragged on, regulators on both sides of the border have confronted difficult tradeoffs regarding the competing interests of farmers, industrialists, and ordinary residents, as well as the moral imperative to practice prudent stewardship of the natural environment.

If these domestic policy dilemmas were not daunting enough, the crisis at the Rio Grande also poses a serious diplomatic challenge. Because the river passes through and collects tributary water from both Mexico and the United States, both states have legitimate claims to the river’s limited flow. This clash of national interests might appear to be a recipe for intractable conflict or hegemonic domination. Yet, remarkably, the opposite is true: for well over a century, the Rio Grande has emerged as a success story for international cooperation. Even as climate change has depleted reservoirs, raising the political and economic stakes on both sides of the border, thus far a spirit of cooperation and compromise has sustained the bilateral partnership.Footnote ⁵

This chapter tells the story of how cooperation has flourished at the Rio Grande in the face of formidable challenges. International law plays a central role in this history. By the middle of the twentieth century, international courts and tribunals were promoting cooperation in disputes over transboundary rivers by decisively rejecting the absolutist conception of national sovereignty. They declared that general principles of equity required riparian states to cooperate with one another to reconcile conflicts between their sovereign rights. These developments in international law greased the wheels for international cooperation over transboundary rivers, helping to avert and defuse conflicts during an era when demand for fresh water was increasing exponentially.

Abandoning Absolute Sovereignty

The Rio Grande is one of 276 transboundary rivers that collectively serve 2.8 billion people – approximately 40 percent of the world’s population. Transboundary river basins, also known as “international watercourses,”Footnote ⁶ occupy nearly half of the earth’s land surface and account for roughly 60 percent of global river flow.Footnote ⁷ The fresh water that flows through these rivers is vital to human survival and economic development, facilitating agriculture, industry, transportation, electricity generation, and other uses.

Transboundary rivers have been at the center of international disputes for millennia. The earliest recorded international treaty addresses tensions between two Ancient Sumerian city-states over the Euphrates River in approximately 2,500 BCE. Since then, political communities have concluded thousands of agreements on the use and management of transboundary rivers.Footnote ⁸ Disputes over these agreements have also led to international arbitration and adjudication, including an advisory opinion and two judgments in contentious cases from the Permanent Court of International Justice (PCIJ), the first international tribunal with general jurisdiction (i.e., authority to hear any kind of case brought before it that is amenable to international adjudication).Footnote ⁹

Notwithstanding the importance of transboundary rivers to human flourishing, the international legal norms governing them were unsettled at the turn of the twentieth century. This uncertainty was attributable in part to a paradox at the heart of the then-prevailing theory of absolute sovereignty. Recall from Chapter 1 that Grotius conceptualized states as possessing exclusive authority and proprietary interests over their own sovereign territory, as well as the prerogative to judge the legality of their own actions for themselves. In disputes over transboundary rivers, upstream states invoked the absolutist conception of territorial sovereignty to support their position that they could use transboundary rivers however they pleased, including by diverting water for domestic irrigation. But downstream states also relied on territorial sovereignty to defend their national interests. In their view, sovereignty entailed the right to absolute territorial integrity, including the unimpaired natural flow of fresh water from upstream sources. How to choose between these dueling theories of sovereign rights – known today as “absolute territorial sovereignty” and “absolute territorial integrity” – was by no means obvious under the prevailing Grotian theory of sovereignty. Consequently, upstream and downstream riparians could each plausibly claim that international law authorized them to dictate how a transboundary river running through their borders should be utilized.

A nineteenth-century dispute between Mexico and the United States over the Rio Grande illustrates this dilemma.Footnote ¹⁰ In July 1848, the United States and Mexico concluded the Mexican-American war by signing the Treaty of Guadalupe Hidalgo.Footnote ¹¹ The treaty designated the deepest channel of the Rio Grande as the boundary line between the two countries for 1,255 miles, and it prohibited both parties from constructing “any work that may impede or interrupt” navigation along this section of the river without the other party’s consent.Footnote ¹² As time wore on, diversions of the river by American farmers depleted the Rio Grande to the point that Mexico felt constrained to file a formal diplomatic protest. In October 1894, Mexico’s chief representative to the United States, Matías Romero, sent a note to US Secretary of State Walter Q. Gresham asserting the “urgent necessity” to address the United States’ “taking of water from the Rio Bravo (Rio Grande) del Norte, which has so seriously affected the existence of the frontier communities for several miles below [Ciudad Juárez]” that they “may be annihilated.” Romero argued that further discussions between the countries should focus on maintaining “the equitable division of the waters of the river.”Footnote ¹³

Responding two weeks later, Gresham disputed Romero’s factual assertion that American irrigation – rather than natural drought – had diminished the Rio Grande’s flow.Footnote ¹⁴ At Gresham’s request, US Attorney General Judson Harmon provided a legal opinion that vigorously defended the United States’ sovereign right to use the Rio Grande as it saw fit, without regard to Mexico’s rights and interests. Harmon explained that the Treaty of Guadalupe Hidalgo did not prohibit the United States from diverting water for irrigation, as long as these diversions did not impede navigation. Turning next to principles of general international law, Harmon emphasized that the “fundamental principle of international law is the absolute sovereignty of every nation, as against all others, within its own territory.”Footnote ¹⁵ He then quoted a passage from Chief Justice John Marshall’s opinion for the US Supreme Court in Schooner Exchange v. McFaddon:

In Harmon’s view, the United States’ prerogative to use as much of the Rio Grande as it wished reflected two basic principles of international law: (1) the “necessarily exclusive and absolute” nature of its territorial sovereignty, and (2) the voluntarist principle (later associated with The Lotus Case) that any limitations on state sovereignty must be attributable to state consent. Thus, because the United States had not consented to limit its use of the Rio Grande for irrigation, it was not violating international law.

Harmon’s defense of absolute territorial sovereignty – the so-called “Harmon Doctrine” – supplied legal cover at a moment when the United States was anxious to preserve existing irrigation works and parry Mexican claims for monetary reparations. The opinion might have advanced these objectives, but its legal analysis was highly problematic from the start. If every state had “exclusive and absolute” jurisdiction over its own territory, as Harmon supposed, then what about Mexico’s territorial sovereignty? Surely Mexico could also claim “full and complete” authority to ensure its own self-preservation by guaranteeing the Rio Grande’s uninterrupted flow through its territory? Allowing the United States to divert the river without Mexico’s consent would, in the Chief Justice’s words, “imply a diminution of [Mexico’s] sovereignty to the extent of that restriction, and an investment of that sovereignty to the same extent in [the United States]” – a result antithetical to Mexico’s sovereignty. Yet, how could Mexico and the United States both exercise “exclusive and absolute” jurisdiction over the Rio Grande’s flow? The only way to resolve this dilemma without violating the territorial sovereignty of either state would be for Mexico and the United States to either negotiate an agreement or submit to international arbitration.

In fact, this is precisely what happened. Well before Harmon weighed in with his now-infamous opinion, the US State Department pursued negotiations with Mexico.Footnote ¹⁷ US President Grover Cleveland delivered an address to Congress in which he argued that tensions over “the storage and use of the waters of the Rio Grande for irrigation should be solved by appropriate concurrent action of the two interested countries.”Footnote ¹⁸ Congress apparently agreed. Expressing concern that US irrigation practices were “rendering the lands [downstream] arid and unproductive, to the great detriment of the citizens of the two countries who live along its course,” Congress adopted a joint resolution in 1890 urging the President to pursue negotiations with Mexico to resolve the issue.Footnote ¹⁹ Thus, in stark contrast to Harmon’s legal opinion, US foreign policy throughout this period demonstrated respect for Mexico’s sovereign rights and interests and a commitment to resolve the issue through bilateral cooperation.

Rather than proceed unilaterally, the two governments asked the International Boundary Commission, which they had established in 1889, to evaluate the facts on the ground and help them determine “the best and most feasible mode” of regulating the Rio Grande “so as to secure to each country concerned and to its inhabitants their legal and equitable rights in said waters.”Footnote ²⁰ Guided by the Commission’s recommendations, Mexico and the United States concluded a treaty in 1906 “to provide for the equitable distribution of the waters of the Rio Grande for irrigation purposes, and to remove all causes of controversy between them in respect thereto.”Footnote ²¹ Under the treaty, the United States committed to deliver 60,000 acre-feet of water from the Elephant Butte Dam annually, and Mexico agreed to waive legal claims arising from the United States’ diversions.Footnote ²²

Mexico and the United States have continued this cooperative relationship into the present. In 1944, the two states concluded a new treaty in which the United States expressly recognized Mexico’s sovereign interest in utilization of the Rio Grande.Footnote ²³ Each of the states committed to contribute a defined volume of water to the Rio Grande from tributaries within their respective jurisdictions.Footnote ²⁴ The treaty established an International Boundary and Waters Commission (IBWC) to coordinate the planning, construction, and operation of works along boundary waters, including hydropower dams, storage and diversion structures, and flood control measures.Footnote ²⁵ It also contemplated that the parties would work through the IBWC to develop additional bilateral agreements – described as “minutes” – to facilitate continued cooperation and resolve future disagreements related to their transboundary waters.Footnote ²⁶ In the 1960s and 1970s, as demand for water accelerated and both countries struggled to meet their contribution commitments, the IBWC’s minutes focused largely on issues of equitable apportionment. By the 1990s, drought management and ecological preservation became more salient.Footnote ²⁷ Thus, cooperation between Mexico and the United States evolved over time in response to the states’ shifting priorities.

A dispute between Mexico and the United States illustrates the resiliency of this cooperative framework. In September 2020, Texas Governor Greg Abbott delivered a letter to US Secretary of State Mike Pompeo formally complaining that Mexico was close to defaulting on its obligations under the 1944 treaty. At the time, Mexico owed the United States “almost a year’s worth of water” – over 300,000 acre-feet – with only six months remaining until the deadline. When Mexico announced that it would honor its treaty obligation, thousands of pecan farmers converged on the Bolaquilla Dam in northern Mexico. Brandishing sticks and stones, the protesters seized control of the dam and closed its valves in an attempt to preserve the dam’s scarce water for their own parched orchards. Rather than appease the farmers, the Mexican government directed its National Guard to reclaim the dam by force and reopen the valves, leading to violent clashes that claimed the life of a protestor, Yesica Silva.Footnote ²⁸ In the end, despite intense regional resistance, the cooperative relationship between Mexico and the United States prevailed, allowing water to continue to flow to the lower Rio Grande. Although Mexico has since fallen further behind in its obligations under the 1944 treaty and political tensions between communities on either side of the river continue to run high, thus far the two sides have managed to prevent the situation from escalating into further violence.Footnote ²⁹

Reconciling Conflicting Rights

The robust Mexico–US partnership at the Rio Grande demonstrates that international cooperation is possible even when states have divergent interests with respect to scarce resources. It does not yet show, however, that international law affirmatively requires such cooperation, much less what the grounds of such a requirement would be. Beginning early in the twentieth century, however, national courts and international courts and tribunals began to recognize that general principles of law do, in fact, obligate states to cooperate with one another to resolve disputes over transboundary rivers. Through these decisions and supportive state practice, mandatory cooperation became firmly enshrined in the customary international law of transboundary rivers.

In the early twentieth century, the US Supreme Court decided a series of cases supportive of mandatory cooperation involving disputes between states of the United States.Footnote ³⁰ In 1907, Kansas sued Colorado for diverting water from the Arkansas River, allegedly depriving Kansas and its inhabitants of the full volume of water to which they were accustomed.Footnote ³¹ The Court observed that “because Kansas and Colorado are states sovereign and independent in local matters, the relations between them [arguably] depend … upon principles of international law.”Footnote ³² The Court then proceeded to identify the applicable legal principles:

In light of these principles, the Court held that the equal rights of Colorado and Kansas required an “equitable division” of water between the two states.Footnote ³⁴

Similarly, in a 1931 case, New Jersey v. New York,Footnote ³⁵ the Court considered New Jersey’s request for an injunction to prevent New York from channeling water away from the Delaware River and its tributaries toward New York City. In an opinion authored by Justice Oliver Wendell Holmes, the Court acknowledged that

According to Justice Holmes, the goal of reconciling sovereign rights in this manner “always is to secure an equitable apportionment without quibbling over formulas.”Footnote ³⁷

Eight years later, the Italian Court of Cassation confirmed that equitable principles also apply to states under international law. In the Convention of December 17, 1914, France and Italy had established a joint framework for utilization of the transboundary Roya River. France later objected to an Italian firm’s plan to construct a power station on the Italian side of the border.Footnote ³⁸ In deciding in favor of the Italian firm, the Court described the applicable law as follows:

Applying these principles, the Court concluded that international cooperation was required under international law to reconcile the states’ conflicting sovereign rights relative to the Roya.

An arbitral tribunal eventually delivered the most influential statement on mandatory cooperation in the 1957 Lake Lanoux Arbitration.Footnote ⁴⁰ The dispute concerned the rights of France and Spain respectively to waters flowing from Lake Lanoux in the Pyrenees.Footnote ⁴¹ Lake Lanoux is situated entirely in France, but its waters flow into the Carol River, which enters Spanish territory after traveling roughly twenty-five kilometers through France.Footnote ⁴² The Treaty of Bayonne of 1866 established the Franco-Spanish border and contained provisions regulating the use of transboundary watercourses like the Carol River.Footnote ⁴³ Article 8 of the Treaty affirmed that “standing and flowing waters … are subject to the sovereignty of the State in which they are located.”Footnote ⁴⁴ Anticipating that situations could arise in which works in one country might affect waters in the other, Article 11 provided that any proposal “to construct works or to grant concessions which might change the course of the volume of a [transboundary] watercourse” could proceed only after “prior notice” to the other state. The purpose of this requirement was to enable aggrieved states to raise timely objections, thus ensuring that “the interests that may be involved on both sides will be safeguarded.”Footnote ⁴⁵

In 1950, France announced that it would divert some of the waters from Lake Lanoux to develop a hydroelectric project on its own soil. France proposed to return the diverted waters to the Carol River (the natural destination of those waters) through an engineered tunnel.Footnote ⁴⁶ Spain objected to the proposed project, arguing that Article 11 of the Treaty of Bayonne required France to obtain Spain’s consent before proceeding.Footnote ⁴⁷ In response, France invoked Article 8, which affirmed the parties’ sovereign jurisdiction over “standing and flowing waters” within their borders. France argued that in any event Spain would suffer no harm from the project because all of the diverted water would return to the Carol River before it crossed into Spain.Footnote ⁴⁸

The Tribunal emphatically rejected the suggestion that France must obtain Spain’s consent before diverting water from Lake Lanoux. The Tribunal expressed concern that if Spain had the right to veto such works in French territory, Spain could dominate its neighbor, suppressing France’s “exercise of territorial jurisdiction” through “unconditional and arbitrary opposition” to new development projects.Footnote ⁴⁹ Spain’s argument would exalt territorial integrity to the detriment of territorial sovereignty, subjecting upstream riparians to the unilateral power of downstream riparians. This would place the sovereign rights of France and Spain on an unequal footing in violation of the principle of sovereign equality.

Although the Tribunal rejected Spain’s argument, it confirmed that France was legally obligated to cooperate with Spain to provide equitable utilization of the disputed waters. Accordingly, France could not treat Spanish interests with indifference; rather, it must consult and negotiate with its downstream neighbor in good faith.Footnote ⁵⁰ In this context, “the reality of the obligations thus undertaken is incontestable and sanctions can be applied in the event, for example, of an unjustified breaking off of the discussions, abnormal delay, disregard of the agreed procedures, systematic refusals to take into consideration adverse proposals or interests, and, more generally – in cases of violation of the rules of good faith.”Footnote ⁵¹ In particular, the Tribunal stressed the “necessity to reconcile [conflicting interests] by mutual concessions,”Footnote ⁵² and that to this end “there would thus appear to be an obligation to accept in good faith all communications and contracts which could, by a broad comparison of interests and by reciprocal good will, provide States with the best conditions for concluding agreements.”Footnote ⁵³

More specifically, the Tribunal held that it would not be enough for France, the upstream state, to engage in a mere box-ticking exercise “such as taking note of complaints, protests or representations made by the downstream State.”Footnote ⁵⁴ Instead, “the upstream State is under the obligation to take into consideration the various interests involved, to seek to give them every satisfaction compatible with the pursuit of its own interests, and to show that in this regard it is genuinely concerned to reconcile the interests of the other riparian State with its own.”Footnote ⁵⁵ France had satisfied these obligations by negotiating with Spain in good faith and giving reasonable consideration to Spanish interests by agreeing to restore waters diverted to the Carol River in a manner that would best accommodate Spanish agriculture.Footnote ⁵⁶

Because France’s efforts to cooperate with Spain were carried out within a mandatory legal framework, Spain was not subject to unilateralism on the part of France, notwithstanding the fact that France was exercising sovereign rights over the waterway. Although Spain did not obtain a veto over France’s hydroelectric project, the Tribunal concluded that Spain was entitled to meaningful consultation and equitable accommodation, thus providing a legal bulwark against French unilateralism. In particular, the Tribunal emphasized that French sovereignty over the upstream waterway must not be used to interfere arbitrarily with Spanish interests or to threaten such interference.Footnote ⁵⁷ Spain had argued that diverting water into a hydroelectric project was wrongful because it would make Spain dependent on France for the continued delivery of water from Lake Lanoux.Footnote ⁵⁸ The Tribunal did not reject this argument on principle, but on the grounds that the facts did not bear it out: because France could not shut off the flow of water without causing serious injury to its own interests, any threat to interfere with Spain’s access to water from Lake Lanoux would be an empty one.Footnote ⁵⁹ Accordingly, there was no genuine prospect of France using the proposed hydroelectric project to dominate Spain or interfere with Spain’s territorial integrity. The Tribunal concluded that France had adequately respected Spain’s sovereign interests by notifying Spain of the proposed project, engaging in extensive consultation and negotiation, submitting to arbitration, and giving due regard to Spain’s sovereign interests in the shared watercourse.

Legal scholars today often characterize Lake Lanoux as affirming a doctrine of “limited sovereign rights” over international watercourses, but this characterization requires qualification.Footnote ⁶⁰ As noted previously, the Treaty of Bayonne expressly preserved the states-parties’ sovereign authority over their respective territories.Footnote ⁶¹ The Tribunal did not question this proposition. Accordingly, the Tribunal left the parties’ sovereign rights undisturbed but held that each of the parties must exercise their rights in accordance with equitable principles that respect the other’s equal sovereignty.

This approach to reconciling conflicts of sovereign rights resonates with equity’s operation in national legal systems. As Henry Smith has observed, equity constitutes a form of “second-order law” or “meta-law” that formally preserves legal rights but conditions how those rights may be exercised in some contexts.Footnote ⁶² Equitable principles characteristically apply to disputes involving conflicting rights, where the exercise of a right by one party could prejudice others’ rights.Footnote ⁶³ Equity’s response to conflicting rights is to impose second-order “in personam” obligations that “leave the presumptive rights in place and to reconcile them ex post based on an equitable, context-sensitive style of reasoning.”Footnote ⁶⁴ Equity accommodates conflicting rights by constraining how parties may exercise rights to prevent what the civilian legal tradition calls an “abuse of right.” Hence, a state may not abuse its sovereign authority over a transboundary river by unilaterally imposing regulations that effectively subordinate another riparian state’s sovereign authority. Nor may a state divert water from a transboundary river in a manner that would disproportionately impact another state’s sovereign rights to the same resource. Consistent with the dominant proportionality-based approach to adjudicating conflicts of rights,Footnote ⁶⁵ international law calls for apportioning water between riparian states in a manner that accounts for the states’ respective equitable interests.Footnote ⁶⁶ This distinctively equitable approach to conflicts of rights has become “the cornerstone of customary international law” governing the use of transboundary rivers.Footnote ⁶⁷

By placing equitable principles at the heart of its regime governing transboundary rivers, international law aims to mitigate practical inequities generated by its allocation of territory among states. If equitable principles did not apply, upstream states (e.g., France, the United States) might invoke their own territorial sovereignty as a trump justifying the unilateral diversion of water that would otherwise flow to downstream states (e.g., Mexico, Spain). Or economically and militarily powerful downstream states (e.g., Egypt) might cite territorial integrity as a justification for coercing upstream states to refrain from using an equitable portion of transboundary waters (e.g., Burundi, Ethiopia, Uganda). By affirming that equitable principles apply to international rivers, international law bars states from dominating their neighbors by unilaterally dictating the terms upon which these shared resources will be governed and apportioned.Footnote ⁶⁸

Establishing a Community of Interest

Recognizing the uncertainty that surrounded the international law of international watercourses at the dawn of the twentieth century, the eminent Swiss jurist Max Huber identified four possible legal paradigms: absolute territorial sovereignty, absolute territorial integrity, limited territorial sovereignty, and community of interest. The last option – community of interest – would treat an international watercourse (including the primary river and all tributaries) holistically as a unitary common resource.Footnote ⁶⁹ Proponents of the community interest paradigm tend to link the idea to concepts of “internationalization” or “denationalization,” suggesting that transboundary rivers are subject to the joint-stewardship of the entire community of riparian states.Footnote ⁷⁰ Under this approach, no member of the community could claim unilateral jurisdiction over a transboundary river, but each would have an equal right to use the river, and each would have equal voice in collective governance.

In its first case on the merits, the PCIJ applied the community of interest paradigm to the Oder, a river that presently traverses the territory of the Czech Republic, Germany, and Poland. Under the Treaty of Versailles, an international commission was responsible for regulating navigation on the Oder.Footnote ⁷¹ The question presented in The River Oder Case was whether the commission’s jurisdiction extended to certain tributaries of the Oder in Polish territory. Purporting to summarize “the principles governing international fluvial law in general,” the Court indicated that

Decades later, the International Court of Justice (ICJ) would cite this passage from The River Oder Case with approval in Gabčikovo-Nagymaros v. Hungary, asserting that the subsequent “development of international law has strengthened this [community of interest] principle for non-navigational uses of international watercourses as well.”Footnote ⁷³

The community of interest paradigm aptly describes some treaty regimes, like the Mexico–US partnership at the Rio Grande, which establish international commissions to govern watercourses holistically for the shared benefit of riparian states. It also helps to make sense of watercourse treaties (or provisions thereof) that are designed to promote environmental conservation, sustainability, and intergenerational equity. The purpose of these agreements is to remove matters of common concern from the unilateral jurisdiction of individual states and commit those matters instead to the joint stewardship of a community of riparian states.Footnote ⁷⁴ Within a community of interest regime, each state must cooperate with the rest of the community to achieve the regime’s objectives, while sharing equitably in the associated benefits and burdens. Significantly, because community of interest regimes are premised on sovereign equality, they are subject to the same equitable principles that apply in conflict of rights cases like Lake Lanoux. In both contexts, states must share relevant information, seek consensus through consultation and negotiation, and, if all else fails, resort to peaceful third-party dispute resolution.

Most transboundary rivers have not been fully internationalized through treaties that establish a community of interest.Footnote ⁷⁵ The reason why states have not concluded more treaties is not hard to imagine. States are often reluctant to relinquish their territorial sovereignty. They do not necessarily trust neighboring states as prospective partners. They might hesitate to conclude agreements that could lock in long-term disadvantages or strengthen a competitor. When states decline to establish a community of interest regime for these or other reasons, Lake Lanoux’s customary default rule applies: each state retains its sovereign rights but must exercise those rights in a manner that satisfies equitable principles.

Codifying Mandatory Cooperation

International watercourse treaties often codify aspects of Lake Lanoux’s customary default rules. In some instances, these agreements have sustained productive international partnerships even among otherwise bitter regional rivals. A striking example is the Indus Waters Treaty of 1960.Footnote ⁷⁶ Originating on the Tibetan plateau, the Indus River travels 1800 miles through India and Pakistan, sustaining the lives and livelihoods of approximately 215 million people throughout its basin. Following the 1947 partition of India and Pakistan, the World Bank averted possible hostilities between the two states by brokering an agreement that has held firm for over sixty years.Footnote ⁷⁷ Rather than treat the Indus River Basin as a unitary system under a community of interest regime, India and Pakistan elected to divide the basin’s waters equitably, with India taking the three eastern rivers (the Ravi, Beas, and Sutlej) and Pakistan the three western rivers (the Indus, Jhelum, and Chenab), subject to India’s right to use some water for irrigation, hydropower generation, and other purposes before the western rivers enter Pakistan.Footnote ⁷⁸ The two states also agreed to develop dams, canals, and other works (bankrolled largely by the World Bank) to increase the total volume of water available for agriculture, electricity generation, and other uses.Footnote ⁷⁹ The treaty establishes an orderly process for information-sharing, consultation, and dispute resolution through a Permanent Indus Commission.Footnote ⁸⁰ If the commissioners fail to reach agreement, the parties may jointly submit unresolved “differences” either to a neutral expert who is a highly qualified engineer or to the Permanent Court of Arbitration (PCA).Footnote ⁸¹ Against all odds, this cooperative framework between India and Pakistan has survived three wars (1965, 1971, 1999), a nuclear arms race, intensifying nationalism, and a host of other challenges,Footnote ⁸² though its future remains fragile in light of enduring tensions between the two historic rivals.Footnote ⁸³

Another important codification of mandatory cooperation is the UN Economic Commission for Europe’s 1992 Convention on the Protection and Use of Transboundary Watercourses and International Lakes, also known as the “Helsinki Convention.”Footnote ⁸⁴ Following the devastating 1986 Sandoz chemical spill, which dyed the Rhine River blood red, wiping out flora and fauna for hundreds of miles, European countries cooperated to establish an “ecosystem-oriented, holistic approach to the sustainable use and integrated management of freshwater resources in Europe.”Footnote ⁸⁵ The keystone of this effort is the Helsinki Convention, which requires state-parties to “prevent, control, and reduce pollution of waters causing or likely to cause transboundary impact”; “ensure that transboundary waters are used with the aim of ecologically sound and rational water management, conservation of water resources and environmental protection”; “ensure that transboundary waters are used in a reasonable and equitable way”; and “ensure conservation and, where necessary, restoration of ecosystems.”Footnote ⁸⁶ The Convention also obligates states-parties to “cooperate in the conduct of research into and development of effective techniques for the prevention, control and reduction of transboundary impact,”Footnote ⁸⁷ and to practice the “widest exchange of information, as early as possible, on issues covered by the provisions of this Convention.”Footnote ⁸⁸ The Helsinki Convention makes international cooperation mandatory by declaring that states-parties “shall on the basis of equality and reciprocity enter into bilateral or multilateral agreements or other arrangements” on a wide range of issues “in order to define their mutual relations and conduct regarding the prevention, control and reduction of transboundary impact.”Footnote ⁸⁹ Each of these features of the Helsinki Convention affirms states’ joint stewardship over the sustainable use and environmental protection of transboundary rivers.

Perhaps the most important codification of mandatory cooperation for transboundary rivers is the landmark 1997 Convention on the Law of Non-Navigational Uses of International Watercourses (the UN Watercourses Convention).Footnote ⁹⁰ Article 5 endorses the principle of equitable and reasonable utilization by providing that states-parties “shall in their respective territories utilize an international watercourse in an equitable manner … taking into account the interests of the watercourse States concerned, consistent with adequate protection of the watercourse.”Footnote ⁹¹ Factors relevant to the equitable apportionment of water include a river’s natural characteristics, the social and economic needs of riparian states, how usage affects other states, and the need for conservation and efficient use of water resources.Footnote ⁹² The Convention also obligates states “when utilizing an international watercourse in their territories, [to] take all appropriate measures to prevent the causing of significant harm to other watercourse States.”Footnote ⁹³

To foster international equity and prevent avoidable harm, the UN Watercourses Convention obligates states to “cooperate on the basis of sovereign equality, territorial integrity, mutual benefit and good faith in order to attain optimal utilization and adequate protection of an international watercourse.”Footnote ⁹⁴ This general obligation entails specific duties to exchange data and information on the conditions of a watercourse,Footnote ⁹⁵ including planned works that might adversely affect other riparian states.Footnote ⁹⁶ In addition, the Convention requires states-parties to consult and negotiate with one another “in good faith,” respecting the principle of sovereign equality by “pay[ing] reasonable regard to [others’] rights and legitimate interests.”Footnote ⁹⁷ If consultation and negotiation do not produce agreement, states-parties must “seek a settlement of the dispute by peaceful means.” Options for peaceful dispute resolution include recourse to an impartial factfinder; the good offices, mediation or conciliation of a third party; submission to a joint watercourse institution; international arbitration; or adjudication in the ICJ.Footnote ⁹⁸ These features of the UN Watercourses Convention codify the customary duties of mandatory cooperation.Footnote ⁹⁹

Managing Entrenched Disputes

When states fail to agree on mutually acceptable terms of cooperation for a transboundary river, this can lead to a protracted stalemate. Entrenched disputes over transboundary rivers are not necessarily the product of bad faith. In some cases, neighboring states may disagree in good faith about the ingredients of an equitable solution. They may prefer different dispute-resolution mechanisms (e.g., mediation, arbitration, adjudication) or institutions (e.g., ICJ, PCA, regional courts). While international dialogue can help to resolve discord between states, in some instances it can harden points of disagreement.Footnote ¹⁰⁰ When this occurs, transboundary river disputes can easily drag on without the expectation of an immediate resolution.

Some of the world’s most important watercourses have become mired in entrenched disputes. The iconic Nile River Basin, which covers over three million square miles and feeds 250 million people, illustrates this problem.Footnote ¹⁰¹ By 2050, the combined population of Nile Basin riparian states is expected to reach one billion, straining the basin’s capacity to meet the population’s basic needs for fresh water.Footnote ¹⁰² For generations, the eleven states within the Nile River Basin have debated how to apportion its finite waters. Citing historical practice, colonial-era treaties, and its continuing needs, Egypt has asserted the right to use over 55 percent of the Nile’s annual flow. Sudan has also claimed preferential rights to Nile Basin waters.Footnote ¹⁰³ However, as upstream riparians have grown in population, political influence, and the ability to attract foreign investment for hydropower and irrigation projects, the reaching claims of Egypt and Sudan have encountered increasingly stiff resistance.

In 2010, multilateral discussions among Nile Basin states produced the Nile Basin Cooperative Framework Agreement (CFA), a treaty that seeks to “promote integrated management, sustainable development, and harmonious utilization of the water resources of the Basin, as well as their conservation and protection for the benefit of present and future generations.”Footnote ¹⁰⁴ Modeled after the UN Watercourses Convention, the CFA embraces the general principles of equitable and reasonable utilization, avoiding significant harm, the preservation of endangered ecosystems, good faith consultation and cooperation, and mandatory dispute resolution.Footnote ¹⁰⁵ The CFA specifically affirms “[t]he principle of cooperation between States of the Nile River Basin on the basis of sovereign equality, territorial integrity, mutual benefit and good faith in order to attain optimal utilization and adequate protection and conservation of the Nile River Basin and to promote joint efforts to achieve social and economic development.”Footnote ¹⁰⁶ Notably, the CFA also invokes the “community of interest” concept as a guiding principle, calling into question the sovereignty-based claims of Egypt and Sudan.Footnote ¹⁰⁷ To date, only seven states have signed on to the CFA (Burundi, Ethiopia, Kenya, Rwanda, South Sudan, Tanzania, Uganda), leaving four holdouts (Democratic Republic of the Congo, Egypt, Eritrea, and Sudan).Footnote ¹⁰⁸ The fact that so many downstream states have declined to endorse the CFA leaves the Nile’s future in limbo, despite growing acceptance on both sides that equitable principles constitute the applicable international lawFootnote ¹⁰⁹ and despite burgeoning cooperation with respect to some issues of common concern, such as flood control and environmental conservation.Footnote ¹¹⁰

Another well-known example of an entrenched dispute is the Gabčikovo-Nagymaros Case.Footnote ¹¹¹ In 1993, Hungary and Slovakia sought the ICJ’s assistance in resolving a dispute over Hungary’s unilateral suspension of a joint-venture between the two countries to develop a system of locks and hydroelectric power plants on the Danube River.Footnote ¹¹² Hungary argued that the project negatively impacted its legal interest and the international community’s collective interest in preserving the river’s ecological health.Footnote ¹¹³ Slovakia contended, in turn, that Hungary’s actions violated a treaty between the two countries.Footnote ¹¹⁴ After concluding that both parties had violated their international legal obligations, the ICJ sent the dispute back to the parties with the instruction to “find an agreed solution” through “good faith” negotiation.Footnote ¹¹⁵ Although Slovakia eventually agreed to discontinue proceedings in the ICJ, for nearly two decades the two sides made little progress in negotiations, raising the specter of perpetual deadlock.Footnote ¹¹⁶

International law responds to entrenched disputes like these by imposing special requirements of mandatory cooperation. First, as long as disputes remain unresolved, states must continue to explore dispute resolution mechanisms in good faith until they find a successful avenue for achieving an equitable resolution.Footnote ¹¹⁷ Second, although states may take provisional steps to secure their legal interests once it becomes clear that an impasse has been reached,Footnote ¹¹⁸ they must notify other interested parties of such measures,Footnote ¹¹⁹ maintain a continuous process of dialogue to ensure that their provisional measures do not foreclose a multilateral solution,Footnote ¹²⁰ and avoid any actions that would “establish a fait accompli capable of prejudicing the outcome of negotiations.”Footnote ¹²¹ The last requirement is especially critical as applied to transboundary rivers: states must refrain from constructing dams, diverting tributaries, and engaging in other invasive works that could cause permanent and irreversible harm to other riparian states’ interests and the natural environment.Footnote ¹²² These obligations are necessary to reconcile sovereign equality and joint stewardship with the often-slow pace of international dispute resolution.

The Promise and Perils of Mandatory Cooperation

As the twenty-first century rolls onward, fresh water might be insufficient in some regions to meet the needs of swelling populations during an era of climate change and rapid economic development. Experts anticipate that by mid-century, 3.1 billion people will live in urban areas with seasonal water shortages.Footnote ¹²³ International cooperation will be essential in this perilous new world of freshwater scarcity to respect, protect, and fulfill human rights, while safeguarding international peace and security.

Regrettably, international cooperation can also aggravate some of the very problems it aspires to solve. Consider the majestic Mekong River, which rises in China and traverses Laos, Myanmar, Thailand, and Cambodia before draining into the South China Sea through Vietnam’s sprawling “Nine Dragon” river delta. Since the early 1990s, a spirit of robust regional cooperationFootnote ¹²⁴ and an influx of foreign investment have enabled states to construct over three hundred hydroelectric dams along the Mekong.Footnote ¹²⁵ This cooperative ethos has quickened the pace of development and enriched elites throughout the river basin, but at a terrible human and environmental cost. Dams have cut off the natural flow of nutrient-rich silt from China, endangering rice production and inland fisheries along the river’s course. Eighty percent of the inhabitants of the Mekong River Basin – over sixty million people – depend upon these dietary staples for survival. Meanwhile, the basin’s vibrant biodiversity, with over 20,000 types of plant and nearly 2,500 animal species, including freshwater dolphins and giant catfish, is tilting rapidly toward ecological collapse. Thus, national authorities in Mekong states have harnessed international cooperation to achieve economic development at the expense of fragile ecosystems and the most vulnerable members of their societies.Footnote ¹²⁶

Given that international cooperation has caused the Mekong’s ecological crisis, it might seem counterintuitive to recommend more international cooperation as a solution. But multilateral engagement is the only plausible and potentially legitimate path to save the Mekong. The environmental harm wrought by proliferating dams cannot be reversed by any single state unilaterally; it requires collective action by the entire community of riparian states – including China, which has invested heavily in dam construction throughout the region.Footnote ¹²⁷ Mekong states will have to share the costs and benefits of environmental conservation. To determine what equity and environmental stewardship require in this context, they must collect and share information regarding relevant factors such as their respective dependence on hydropower, the ecological health of the river, and the impact of dams and other works on their domestic agriculture and fishing. They will have to negotiate in good faith or agree to resolve their differences through third-party dispute resolution. In short, they will have to jointly embrace mandatory cooperation.

A Fighting Chance

On June 19, 2023, national delegates from nearly 200 countries gathered under the soaring rotunda of the UN’s General Assembly Hall in New York City to approve, by consensus, a landmark agreement for the conservation and sustainable use of marine life.Footnote ¹ Commonly known as the “High Seas Treaty” or the “Biodiversity Beyond National Jurisdiction (BBNJ) Agreement,” the treaty represents the culmination of over a decade of multilateral negotiations.Footnote ² At its heart is an ambitious framework for establishing large marine protected areas in the high seas – a critical step toward achieving the United Nations’ goal of effectively conserving and managing 30 percent of the earth’s oceans by 2030.Footnote ³

This diplomatic breakthrough arrived not a moment too soon. As UN Secretary-General António Guterres reminded the assembled delegates, marine species in the twenty-first century face a harrowing number of existential threats, including warming oceans, shifting weather patterns, ocean acidification, and the disruption of coastal ecosystems. To make matters worse, human population growth and the rise of modern industrial fishing technologies have generated overfishing on an unprecedented scale, with over a third of global fish stocks subject to unsustainable harvesting.Footnote ⁴

While acknowledging the daunting challenges ahead, Guterres praised the delegates for having “pumped new life and hope to give the ocean a fighting chance”:

In celebrating the “spirit of multilateral cooperation” that produced the High Seas Treaty, however, the Secretary-General glossed over an important point: international cooperation in this case was not merely good policy, it was also a legal obligation. For decades leading up to the High Seas Treaty, international courts and tribunals had affirmed that the law of the sea required states to cooperate with one another to ensure the conservation and sustainable use of marine resources.Footnote ⁶ Aided by the UN International Law Commission (ILC), states had also codified this requirement to cooperate in a multilateral convention with near-universal membership.Footnote ⁷ Thus, by working together to develop the High Seas Treaty, members of the General Assembly were not writing on a blank slate; rather, they were taking steps to fulfill a longstanding legal obligation to cooperate for the conservation and management of oceanic resources.

International law did not always require states to cooperate in this way. Prior to the middle of the twentieth century, the conventional wisdom among international lawyers was that states were free to use and exploit oceanic resources however they wished, without regard to the rights or interests of other states or the natural environment. The rise of mandatory cooperation during the twentieth century therefore marked a sharp break with centuries of precedent – a startling revolution in the law of the sea. As the law of the sea is one of the oldest and most important fields of international law, the historical developments recounted in this chapter serve as a bellwether for mandatory cooperation’s emergence in international law more generally.

The Battle of the Books

On February 25, 1603, a violent episode in the Straits of Singapore sent shock waves around the world, rattling the capitols of Europe. In a stunning challenge to Portuguese naval supremacy in the Far East, three Dutch ships ambushed a massive Portuguese treasure ship, the Santa Catarina, capturing a cargo worth 3.5 million guilders – “more than 60 percent of the average annual expenditures of the English government at the time.”Footnote ⁸ When the Santa Catarina eventually reached Amsterdam, the local admiralty board declared the seizure “good prize” and sent the ship with its lavish cargo of gold, silks, and spices to auction for the benefit of the Dutch East India Company.Footnote ⁹

Seeking to bolster the legal case for the Santa Catarina’s capture, the Dutch East India Company enlisted Hugo Grotius to prepare a supportive legal opinion. Just twenty-one years old at the time, Grotius had already achieved fame as “the Miracle of Holland” for his formidable intellect, dazzling erudition, and literary flair.Footnote ¹⁰ Applying these prodigious talents to the Dutch East India Company’s legal defense, Grotius argued that the laws of war permitted the Santa Catarina’s seizure in response to Portugal’s illegal efforts to prevent Dutch ships from transiting through the East Indies.Footnote ¹¹ Grotius asserted that Portugal could not claim exclusive dominion over the seas surrounding the Straits of Singapore because the sea, by its nature and according to the custom of nations, was not amenable to possession.Footnote ¹² The ocean was not subject to possession in the same manner as land, because its constant motion prevented states from demarcating clear maritime boundaries.Footnote ¹³ Moreover, the abundant and apparently inexhaustible character of oceanic resources meant that no state could justly exclude others from sharing in the oceans’ bounty.Footnote ¹⁴ To prevent any nation from sailing and fishing on the sea, when those activities pose no threat to the state’s own interests, would reflect a “brainsick covetousness” incompatible with natural law and state practice since antiquity, Grotius claimed.Footnote ¹⁵ The sea therefore constituted a global commons (res communis) outside the scope of national jurisdiction and immune from claims to national appropriation. Portugal’s defiance of these principles amounted to a just cause of war.

In 1609, Grotius published a slim pamphlet advancing these arguments against national appropriation of the seas under the title Mare Liberum (The Free Sea).Footnote ¹⁶ The pamphlet sparked a political firestorm. The Vatican placed Mare Liberum on its list of banned books, perceiving the tract (accurately) as an assault on the Papal Bull of Pope Alexander VI, which had partitioned the globe into two spheres – one for Portuguese expansion to the east and the other for Spanish conquest to the west.Footnote ¹⁷ Iberian scholars rushed to defend their nations’ claims to dominion over the high seas.Footnote ¹⁸ British publicists also sparred with Grotius, seeking to defend their crown’s claims to exclusive dominion over the English Channel and the North Sea.Footnote ¹⁹ As clashes between Grotius’s supporters and opponents dragged on over the course of the seventeenth century, the debate came to be known as “the battle of the books” (la bataille des livres).Footnote ²⁰

Among those who opposed Grotius’s vision of the free sea, his most influential and forceful critic was John Selden, the great English lawyer whom John Milton hailed as “the chief of learned men reputed in this land.”Footnote ²¹ In a provocatively titled 1636 treatise, Mare Clausum (The Closed Sea), Selden dismantled Grotius’s historical and empirical claims. He argued persuasively that maritime powers since antiquity had often claimed certain maritime zones as their exclusive possession, including the seas surrounding the British Isles.Footnote ²² He also observed that some maritime resources, such as coastal fisheries and gems and pearls in the seabed, were clearly finite and exhaustible. Accordingly, he argued that states could justifiably claim dominion over regions of the sea where such resources were located.Footnote ²³

Under pressure from his critics, Grotius eventually conceded that states could acquire sovereign rights over certain maritime zones, such as bays and straits, where they had established effective control through a sustained naval presence.Footnote ²⁴ By the eighteenth century, this principle of possession through effective control produced the “cannon shot rule” whereby coastal states were allowed to claim sovereign rights over a “territorial sea” extending three miles from their shore.Footnote ²⁵ Beyond this three-mile zone, however, Grotius’s free sea became the undisputed customary norm. Although Selden arguably advanced the stronger argument from historical practice, Grotius’s vision of the high seas as a global commons held greater appeal for subsequent generations who viewed blue water as the indispensable gateway to international commerce and domestic prosperity.Footnote ²⁶

The Tragedy of the Free Sea

Given the sharp divisions between Grotius and Selden, it is easy to overlook that their dueling accounts of the law of the sea shared a basic assumption about the juridical character of state rights and powers. Both accounts assumed that a state may exercise its rights and powers under the law of the sea however it liked, without regard to the competing rights or interests of foreign states, indigenous peoples, and the global environment. According to Selden, a state that established dominion over a closed sea could exclude foreign vessels from fishing or traversing its waters for any reason or no reason at all. Treating the sea as a global commons, as Grotius advocated, invited unilateralism of a different kind: all states were free to exploit oceanic resources to their hearts’ content – even if this endangered fish stocks, jeopardized fragile ecosystems, and undermined other peoples’ economic and humanitarian interests. Although Grotius and Selden disagreed about the extent to which states could assert proprietary interests over the sea, they both assumed that if states held any rights and powers under the law of the sea, then the exercise of those rights and powers would be left to the states’ absolute discretion. For Grotius, Selden, and their contemporaries, this prerogative to exercise rights and powers unilaterally defined what it meant to be sovereign.Footnote ²⁷ Conceptualizing sovereign rights and powers in this manner facilitated European colonialism by empowering the great naval powers of the day to travel, fish, and dominate international commerce without regard to local needs elsewhere in the world.

The drawbacks of this unilateralist model of state sovereignty came into sharper relief over time as states confronted a dynamic that the twentieth-century ecologist Garrett Hardin famously described as “the tragedy of the commons.”Footnote ²⁸ Hardin’s key insight was that in a world with an expanding human population and finite natural resources, resources held in common will inevitably trend toward depletion as individuals pursue their own rational self-interest.Footnote ²⁹ “Ruin is the destination toward which all men rush, each pursuing his own best interest in a society that believes in the freedom of the commons,” Hardin lamented. “Freedom in a commons brings ruin to all.”Footnote ³⁰

By the end of the nineteenth century, the tragedy of the commons had begun to take a serious toll on global fisheries, prompting some national authorities to reconsider their commitment to the Grotian free sea. An early case involved a dispute between Canada and the United States over resources in the Bering Sea. Hundreds of miles east of Anchorage lie the Pribilof Islands, an inhospitable cluster of volcanic outcroppings which the United States acquired from Russia when it purchased Alaska in 1867.Footnote ³¹ The Pribilof Islands are noteworthy as the breeding ground of the North Pacific fur seal, the largest fur seal group in the world.Footnote ³² Throughout the nineteenth and early twentieth centuries, the fur seal’s sleek brown coat was highly prized as a decorative element in aristocratic fashion, adorning the “jackets of Gilded Age heiresses” in the United States and “Belle Epoque aristocrats” in Europe, as well as appearing “draped over elegant shoulders in cities like Melbourne, Cape Town, or Canton.”Footnote ³³ During the summer mating season, North Pacific fur seals congregated on the islands’ rocky shores. Hunters on shore could cull uncoupled males from the herd without materially impacting the population’s overall birth rates.Footnote ³⁴ As soon as the seals began their southward winter migration in search of warmer havens, however, they entered the high seas – a global commons where tragedy awaited. By the 1880s, a fleet of eighteen British Columbian schooners shadowed fur seals along their migration route, using shotguns and explosives to decimate the herd, driving the North Pacific fur seal to the edge of extinction.

The United States responded to this threat aggressively, in the process testing the limits of its authority under international law. In 1881, the US Treasury Department declared the entire Bering Sea a mare clausum over which the United States claimed exclusive dominion. American revenue cutters then began seizing Canadian schooners outside the three-mile territorial sea though inside the Bering Sea.Footnote ³⁵ Relations between the two countries grew increasingly fractious, with the Canadian press and sealing industry calling on the powerful Royal Navy to intervene to protect its fishing rights under international law.Footnote ³⁶

Seeking to defuse escalating tensions, the United Kingdom (representing Canada) and the United States submitted the North Pacific fur seal dispute to international arbitration. The arbitrators who gathered at the Quai d’Orsay in Paris to resolve the dispute reflected the high political stakes: they included the newly elected Prime Minister of Canada Sir John Thompson, British Judge Lord Hannen, US Supreme Court Justice John Marshall Harlan, and Alabama Senator John Morgan.Footnote ³⁷ The legal issues essentially boiled down to a single core question: did international law authorize the United States to regulate sealing outside its three-mile territorial sea?Footnote ³⁸ Under the prevailing Grotian consensus, the answer to this question was clear: centuries of state practice and opinio juris dictated that waters beyond the territorial sea constituted a res communis that was not susceptible to state appropriation or regulation. The tribunal therefore concluded that the United States “has not any right of protection or property in the fur-seals frequenting the islands of the United States in [the] Behring Sea, when such seals are found outside the ordinary three-mile limit.”Footnote ³⁹ Under international law, British Columbian sealers were free to pursue their rational self-interest by hunting the endangered North Pacific fur seals in the Bering Sea whenever and however they wished.

Ecological disaster was averted only by a second feature of the parties’ compromis: anticipating that the United States’ argument for a mare clausum would fail, the parties also empowered the arbitral tribunal to establish binding regulations to promote sustainable sealing practices.Footnote ⁴⁰ Here the arbitration proved its value. The arbitrators prohibited both states from killing or capturing North Pacific fur seals in waters located within sixty miles of the Pribilof Islands, where female fur seals sought food for their young. They also outlawed hunting on the high seas anywhere in the Pacific Ocean, including the Bering Sea, during the early summer when the fur seal herd migrated to their island rookeries.Footnote ⁴¹ Within the seasons and maritime zones where fur seal hunting was permitted, the arbitrators’ regulations authorized hunting only by licensed sailing vessels,Footnote ⁴² and they prohibited sealers from deploying nets, fire arms, or explosives.Footnote ⁴³ By accepting and implementing these regulations in a spirit of cooperation, the parties prevented the North Pacific fur seal from being hunted out of existence.

Significantly, the parties to the North Pacific Fur Seal Case averted disaster not by relying on the international law of the sea, but instead by voluntarily embracing bilateral regulatory cooperation. Consistent with Hardin’s theory of the tragedy of the commons, Grotius’s free sea led the two states to the brink of ecological catastrophe and the near-collapse of their sealing industries. This outcome was the predictable consequence of treating wildlife in the Bering Sea as a res communis subject to unilateral state exploitation. Had the British Columbian fleet continued to hunt fur seals indiscriminately along their migration routes through the Bering Sea, as they were entitled to do under international law, the North Pacific fur seal might well have gone extinct. Only by setting aside the rights granted to them under international law and voluntarily submitting to binding arbitration were the parties able to chart a course toward sustainable management of the North Pacific fur seal population.

The Tide Turns

Following the North Pacific Fur Seals Case, an American commentator confidently declared:

This prediction could not have been more wrong.

On September 28, 1945, US President Harry Truman issued two proclamations that shattered the Grotian consensus. The first proclamation claimed the natural resources of the seabed and subsoil of the continental shelf alongside the United States’ coastline as being subject to the United States’ exclusive territorial jurisdiction and control.Footnote ⁴⁵ The second proclamation asserted regulatory jurisdiction, but not an exclusive proprietary interest, over certain living resources located in waters above the claimed continental shelf.Footnote ⁴⁶ These unilateral measures catalyzed a global chain reaction, prompting other coastal states to issue their own proclamations asserting sovereign rights to maritime resources beyond their territorial seas. In 1947, Chile and Peru each claimed sovereignty not only over the seabed and subsoil of their appurtenant continental shelf, but also over the super-adjacent waters and associated living resources out to 200 miles beyond their coastlines.Footnote ⁴⁷ Other states followed suit. The Truman proclamations thus set in motion a cascade of unilateral state actions and reactions that collectively unsettled the Grotian consensus regarding the sea’s legal status as a global commons.

This dramatic shift in state practice and opinio juris was motivated, at least in part, by sustainability concerns similar to those that spurred the United States a half-century earlier to declare the Bering Sea a mare clausum. The United States feared that without immediate regulatory intervention, Japanese fishing fleets would destroy salmon fisheries in the Pacific Northwest.Footnote ⁴⁸ Chile and Peru likewise hoped to protect dwindling whale pods along their coasts from predatory foreign fleets.Footnote ⁴⁹ By the 1940s these concerns were widely shared by coastal states. However, the uncoordinated issuance of unilateral proclamations established a patchwork of inconsistent national standards that sat uncomfortably with the customary international law of the sea.Footnote ⁵⁰

The United Nations responded to this jural discord by organizing an international initiative to codify the law of the sea. In 1958, the ILC convened a Conference on the Law of the Sea that produced a set of treaties, known collectively as the Geneva Conventions on the Law of the Seas (GCLS).Footnote ⁵¹ The GCLS formulated new legal standards for the territorial sea and contiguous zone, the high seas, fishing and conservation of the living resources of the high seas, and the continental shelf.Footnote ⁵² Some important coastal states declined to join the GCLS, however, raising questions about whether the Conventions’ provisions had sufficient support in state practice and opinio juris to reflect customary international law.Footnote ⁵³

Two years later, the ILC convened a second Conference on the Law of the Sea at the request of the UN General Assembly. The Conference considered a variety of topics that were not addressed in the GCLS, including the breadth of the territorial sea and the limits of state regulatory jurisdiction over coastal fisheries. The Conference was widely perceived as a failure when the two resolutions adopted at its conclusion left a host of key issues unresolved.Footnote ⁵⁴

Cod Wars

At this crucial transitional moment, a controversy arose in the North Atlantic that profoundly shaped the subsequent development of the international law of the sea. Upon gaining independence from Denmark in 1944, Iceland sought to wrest control of its surrounding waters from predatory foreign fleets that had wreaked havoc on its fisheries.Footnote ⁵⁵ This initiative was a matter of supreme importance to the newly independent state, because fishing constituted the lion’s share of the country’s exports.Footnote ⁵⁶ Iceland’s aspiration to establish sovereignty over its coastal fisheries resonated with the concurrent efforts of formerly colonized peoples elsewhere in the world to achieve national self-determination, economic development, and sovereignty over their natural resources.Footnote ⁵⁷ However, when Iceland followed the lead of other established states in claiming a twelve-mile territorial sea, it encountered stiff opposition from the Federal Republic of Germany (West Germany) and the United Kingdom, which had fished in Icelandic waters for generations.Footnote ⁵⁸

In 1972, Iceland declared its intent to extend its national fishery zone out to fifty nautical miles.Footnote ⁵⁹ British and German fishers initially ignored Iceland’s claim and continued fishing. However, Iceland had developed a device that enabled its coast guard to sever the nets of foreign trawlers. Iceland used this invention to spectacular effect, destroying the nets of sixty-nine British and fifteen West German vessels. In response, the British Royal Navy sent frigates to protect its fishing fleet by ramming and occasionally training live fire on Icelandic coast guard vessels. The ensuing violent confrontations between Iceland and its foreign adversaries, which caused substantial property damage and injuries to sailors and fishers on both sides, came to be known as the Cod Wars.Footnote ⁶⁰

As the conflict over the Icelandic fisheries escalated, the United Kingdom and West Germany each initiated proceedings before the ICJ. Iceland refused to participate, arguing that its decision to claim exclusive fishing rights out to fifty miles was a purely domestic matter over which the ICJ lacked jurisdiction.Footnote ⁶¹ The ICJ disagreedFootnote ⁶² and proceeded to render judgment on the merits in July 1974.Footnote ⁶³

The Court opened its merits judgment by emphasizing that “[t]he delimitation of sea areas has always an international aspect; it cannot be dependent merely upon the will of the coastal State as expressed in its municipal law.”Footnote ⁶⁴ The Court acknowledged that the treaties that emerged from the 1958 and 1960 Conferences on the Law of the Sea left the breadth of a coastal state’s fishery jurisdiction unsettled.Footnote ⁶⁵ The Court therefore rejected Iceland’s position that international law recognized the right to a fifty-mile exclusive fishery zone.Footnote ⁶⁶ However, the Court also concluded that a “general consensus” among states at the 1960 Conference had “crystallized as customary law” the principle that a coastal state enjoys “preferential rights of fishing in adjacent waters” whenever it has established “special dependence on its coastal fisheries.”Footnote ⁶⁷ Given Iceland’s extraordinary economic dependence on its coastal fisheries and the evident need to limit catch levels in order to preserve the fisheries from depletion, the Court agreed that Iceland was entitled to claim such preferential fishing rights.Footnote ⁶⁸

Had the ICJ followed the classical unilateralist model of state sovereignty, its characterization of Iceland’s fishing rights as “preferential” might have been fatal to the competing claims of the United Kingdom and West Germany. The Court could have construed Iceland’s preferential rights as trumps that categorically superseded the competing claims of the United Kingdom and West Germany. Under this approach, Iceland would have been within its rights to exclude British and German fishers from its adjacent waters.

The ICJ, however, adopted a radically different approach. It rejected Iceland’s assertion that the priority accorded to its fishing rights under customary international law meant that it was “free, unilaterally, and according to its own uncontrolled discretion, to determine the extent of [its] rights” vis-à-vis other states.Footnote ⁶⁹ Preferential rights did not operate as trumps, the Court explained: characterizing a “coastal State’s rights as preferential implies a certain priority, but cannot imply the extinction of the concurrent rights of other States.”Footnote ⁷⁰ Instead, “in order to reach an equitable solution of the present dispute it is necessary that the preferential fishing rights of Iceland, as a State specially dependent on coastal fisheries, be reconciled with the traditional fishing rights of the Applicant[s].”Footnote ⁷¹

How, then, should these conflicting rights be reconciled? The ICJ explained that Iceland must “take into account and pay regard to the position of [the United Kingdom and West Germany],” in recognition of their “economic dependence on the same fishing grounds.”Footnote ⁷² Iceland should then seek to “bring[] about an equitable apportionment of the available fishing stocks based on the facts of the particular situation,” according special weight to its own preferential rights, but also taking into account the need for conservation and “the interests of other States which have established fishing rights in the area.”Footnote ⁷³

Far from leaving fishery management to Iceland’s absolute discretion, the Court emphasized that the states concerned must cooperate with one another to determine how Iceland’s preferential rights can be best reconciled with other states’ historically established rights. In particular, the parties must “keep under review the fishery resources in the disputed waters” and “examine together, in the light of scientific and other available information, the measures required for the conservation and development, and equitable exploitation, of those resources.”Footnote ⁷⁴ Following this consultation and exchange of information, Iceland’s preferential rights “are to be implemented by agreement between the States concerned, either bilateral or multilateral, and, in case of disagreement, through the means for the peaceful settlement of disputes provided for in Article 33 of the Charter of the United Nations.”Footnote ⁷⁵ In other words, Iceland and its rivals must pursue “negotiation, enquiry, mediation, conciliation, arbitration, judicial settlement, resort to regional agencies or arrangements, or other peaceful means of their own choice.”Footnote ⁷⁶ The Court explained that this obligation “flows from the very nature of the respective rights of the Parties” – their concurrent rights to a common resource.Footnote ⁷⁷ The Court therefore directed the parties to enter negotiations for the purpose of determining an equitable apportionment of the available fishing stocks.Footnote ⁷⁸

Significantly, the ICJ was quick to acknowledge that its approach to the Icelandic fisheries dispute represented a major departure from the classical model of sovereign unilateralism, as reflected in cases like North Pacific Fur Seals. The Court defended its equitable approach, however, as a modernizing improvement to the law of the sea that was worth celebrating: “It is one of the advances in maritime international law … that the former laissez-faire treatment of the living resources of the sea in the high seas has been replaced by a recognition of a duty to have due regard to the rights of other States and the needs of conservation for the benefit of all.”Footnote ⁷⁹

According to the Court, the law of the sea had entered a new era in which mandatory cooperation based on equitable principles had replaced state unilateralism as the governing legal framework for reconciling states’ rights to oceanic resources.

Delimiting Maritime Boundaries

The Cod Wars were not the only international dispute during this period that gave the ICJ an opportunity to affirm mandatory cooperation in the law of the sea. Several years before the Fisheries Cases, a controversy between Denmark, the Netherlands, and West Germany led the Court to affirm that mandatory cooperation also applied to maritime boundary delimitation.Footnote ⁸⁰

At stake in the case were national claims to resources in the seabed and continental shelf beneath the North Sea.Footnote ⁸¹ During the first Conference on the Law of the Sea, the international community had endeavored to clarify the legal standards that governed such claims. The 1958 Convention on the Law of the Continental Shelf, part of the original GLCS, permitted coastal states to claim exclusive sovereign rights over their adjacent continental shelf.Footnote ⁸² States with opposite or adjacent coastlines were to determine the boundaries between their continental shelf claims by agreement.Footnote ⁸³ Barring “special circumstances,” boundaries between states’ territorial jurisdiction were to be determined by the principle of equidistance.Footnote ⁸⁴ For states with coastlines on opposite sides of a continental shelf, boundaries should ordinarily track “the median line, every point of which is equidistant from the nearest points of the baselines from which the breadth of the territorial sea of each State is measured.”Footnote ⁸⁵ States with adjacent coastlines should determine equidistance by reference to “the nearest points of the baselines from which the breadth of the territorial sea of each State is measured.”Footnote ⁸⁶

Had Denmark, the Netherlands, and West Germany all been parties to the Convention on the Law of the Continental Shelf, the ICJ’s task in the North Sea Continental Shelf Case would have been a relatively straightforward exercise in maritime cartography. What made the case more challenging from a legal perspective was that West Germany had not joined the Convention and disputed the equidistance principle’s applicability to nonparties.Footnote ⁸⁷ The Court agreed with West Germany’s assessment that the Convention’s equidistance principle was “a purely conventional rule,”Footnote ⁸⁸ which “did not embody or crystallize any pre-existing or emergent rule of customary law.”Footnote ⁸⁹ Accordingly, the Court had to determine what customary norms, if any, operated in the Convention’s shadows as default rules for maritime boundary delimitation.

Falling back on “basic legal notions which … have from the beginning reflected the opinio juris in the matter of delimitation,” the Court concluded that customary international law required the parties to resolve their dispute through “agreement … in accordance with equitable principles.”Footnote ⁹⁰ The Court took pains to emphasize that equitable principles did not invite recourse to principles of “abstract justice,”Footnote ⁹¹ nor did it require that coastal states receive an equal or “just and equitable share” of the resources within a continental shelf.Footnote ⁹² For example, countries with a short coastline would not necessarily be entitled to claim the same share of a continental shelf as states with much longer coastlines.Footnote ⁹³ Instead, references to “equitable principles” in this context should be understood as

The ICJ characterized these requirements of mandatory cooperation as “merely a special application of a principle which underlies all international relations” – namely, the general obligation to resolve international disputes peacefully in a spirit of mutual respect and accommodation, rather than through unilateral fiat and coercion.Footnote ⁹⁵ The Court therefore directed the parties to resume negotiations for the purpose of determining to what extent equitable principles would support departing from the equidistance principle to account for West Germany’s exceptionally concave coastline relative to its neighbors, Denmark and the Netherlands.Footnote ⁹⁶

In sum, the North Sea Continental Shelf Case and the Fisheries Jurisdiction Cases affirm that the international law of the sea requires states to cooperate with one another to resolve disputes over maritime resources in accordance with equitable principles. In North Sea Continental Shelf, the Court held that the states must cooperate to resolve an unsettled question regarding the apportionment of national jurisdiction. Should any of the parties impose their preferred solution to the boundary dispute unilaterally, such action would violate the principle of sovereign equality.Footnote ⁹⁷ Mandatory cooperation also applied in the Fisheries Jurisdiction Cases because Iceland and the United Kingdom held concurrent rights to the same resources. In each of these settings, the Court recognized that the only way to harmonize the respective rights of the litigants, while respecting their authority and formal equality as sovereign states, was to direct them to resolve their disputes through negotiation based on equitable principles. With the principle of sovereign equality on the line, directing the parties to negotiate was “a proper exercise of the judicial function,” the Court concluded.Footnote ⁹⁸

Codifying Mandatory Cooperation

Although mandatory cooperation makes brief appearances in the GLCS,Footnote ⁹⁹ it achieves its fullest expression in UNCLOS. With well over 300 articles and nine annexes, this sprawling codex addresses almost every topic imaginable on the law of the sea. Some have characterized UNCLOS as a “synthesis” of Grotius’s mare liberum and Selden’s mare clausumFootnote ¹⁰⁰ because it guarantees universal freedoms on the high seas while also expanding national jurisdiction by, among other things, extending the territorial sea to twelve miles and expanding national jurisdiction over fisheries via a 200-nautical-mile exclusive economic zone.Footnote ¹⁰¹ At a more fundamental level, however, UNCLOS breaks sharply with the classical model of state sovereignty exemplified in the writings of both Grotius and Selden by imposing obligations of mandatory cooperation within every maritime zone beyond the territorial sea.

Requirements to cooperate under UNCLOS can be grouped into three general categories.Footnote ¹⁰² First, whenever states hold concurrent rights or powers over maritime resources, UNCLOS requires them to cooperate in the management of those resources. For example, mandatory cooperation applies when fishing stocks straddle national jurisdictions or migrate from one jurisdiction to another: the states concerned must work together to establish measures necessary to conserve and develop these stocks in order to promote sustainability and optimal utilization.Footnote ¹⁰³ UNCLOS entitles landlocked and geographically disadvantaged states to fish in coastal states’ otherwise exclusive economic zones, but the “terms and modalities” for these activities are to be established through negotiated agreement with coastal states on an equitable basis.Footnote ¹⁰⁴ States that border an enclosed or semi-enclosed sea are required to coordinate their management, conservation, exploration, and exploitation of the sea’s living resources; coordinate protection and preservation of the marine environment; and establish joint research programs for these purposes.Footnote ¹⁰⁵ Likewise, states that use straits and those that border straits must cooperate with one another to maintain navigational and safety aids and prevent and control pollution.Footnote ¹⁰⁶ These measures are designed to ensure that states exercise their sovereign rights and powers under the law of the sea in a manner that reflects due regard for other states’ rights and powers.

Most remarkably, mandatory cooperation applies to states even on the high seas. According to the equitable model enshrined in UNCLOS, a state’s right to navigate and fish on the high seas must be exercised always “with due regard to the interests of other States in the exercise of the freedom of the high seas.”Footnote ¹⁰⁷ Far from enjoying an absolute right that may be exercised unilaterally, as was the case under Grotius’s free sea, UNCLOS requires states to cooperate with one another to establish and implement regulatory measures necessary for the conservation and management of living resources in the high seas.Footnote ¹⁰⁸ This broad obligation to cooperate entails specific requirements to exchange relevant scientific information and data on fish stocks, consult and negotiate with one another, and, “as appropriate, cooperate to establish subregional or regional fisheries organizations” for the purpose of promoting prudent conservation and management of living resources in the high seas.Footnote ¹⁰⁹ In each of these respects, UNCLOS demands that states exercise their rights on the high seas in an equitable manner that reflects due regard for the equal rights of other sovereign states.

Second, UNCLOS reinforces the ICJ’s judgment in the North Continental Shelf Case by confirming that mandatory cooperation governs maritime boundary delimitation. States with opposite or adjacent coasts must set jurisdictional boundaries for the continental shelf and their respective exclusive economic zones “by agreement on the basis of international law … in order to achieve an equitable solution.”Footnote ¹¹⁰ If states struggle to reach agreement on maritime boundaries through bilateral consultation and negotiation, they must seek third-party dispute resolution.Footnote ¹¹¹ Pending a final resolution, states-parties are obligated to proceed “in a spirit of understanding and cooperation,” making “every effort to enter into provisional agreements of a practical nature,” while taking care to avoid actions that would “jeopardize or hamper the reaching of the final agreement.”Footnote ¹¹² UNCLOS thus prohibits states from violating the principle of sovereign equality by dictating the scope of their maritime jurisdiction vis-à-vis other states unilaterally.Footnote ¹¹³

Third, UNCLOS mandates cooperation in settings where oceanic resources are committed to the collective stewardship of the international community as a whole. This category is exemplified most clearly in the convention’s articles governing the use and exploitation of resources from the seabed and ocean floor beneath the high seas.Footnote ¹¹⁴ To underscore the contribution that these articles make to the law of the sea, some additional historical context might be helpful.

Over a decade before UNCLOS arrived on the scene, Maltese Ambassador Arvid Pardo brought a novel proposal to the UN General Assembly: he urged the international community to reserve the seabed and ocean floor beneath the high seas with their valuable deposits of cobalt, copper, lithium manganese, and zincFootnote ¹¹⁵ as a “common heritage of mankind” outside national jurisdiction.Footnote ¹¹⁶ This common heritage concept bore a superficial resemblance to Grotius’s res communis, but Pardo actually had in mind something fundamentally different. Rather than expose the resources of the deep seabed and ocean floor to unilateral exploitation by individual states, Pardo argued that these resources should be exempted from national appropriation. He proposed that the international community establish an international agency to assume exclusive jurisdiction over deep sea resources “as a trustee for all countries,” using profits generated from the area “primarily to promote the development of poor countries.”Footnote ¹¹⁷ Pardo’s ambitious vision, in other words, called for using the resources of the deep sea to level the economic playing field between developed and less-developed states, thus mitigating persistent global inequities that can be traced, at least in part, to international law’s colonialist legacy.

The General Assembly endorsed Pardo’s proposal unanimously in 1970, designating the seabed and ocean floor beyond the limits of national jurisdiction as a “common heritage of mankind” to be “exploited for the benefits of mankind as a whole, and taking into particular consideration the interests and needs of the developing countries.”Footnote ¹¹⁸ Through UNCLOS, the international community further codified this principle and established an institutional framework to operationalize Pardo’s vision.Footnote ¹¹⁹ UNCLOS proclaims the deep seabed and ocean floor and their associated resources “the common heritage of mankind” and affirms that they are “vested in mankind as a whole,” rather than states individually.Footnote ¹²⁰ It then establishes an international organization – the International Seabed Authority – to regulate and manage the resources as a steward or fiduciary of humanity.Footnote ¹²¹ The convention directs the Authority to “provide for the equitable sharing of financial and other economic benefit derived from activities in the Area,” while “taking into particular consideration the interests and needs of developing States and of peoples who have not attained full independence or other self-governing status.”Footnote ¹²² In carrying out these responsibilities, the Authority bears obligations to cooperate with interested states by collecting and carrying out relevant scientific research; to consult, negotiate with, and give due regard to the rights and interests of states that might be effected by its activities; to adopt regulations for protection of human life and the marine environment; and to promote international cooperation for economic development and trade, with special attention to the needs of developing states.Footnote ¹²³

The Authority thus facilitates international cooperation for collective management of the common heritage resources of the deep seabed and ocean floor. When a state harvests resources from the deep sea floor, other members of the international community are entitled under UNCLOS to an equitable share of the proceeds as administered by the Authority.Footnote ¹²⁴ The United States and a handful of other developed states have resisted these features of the Convention, expressing reluctance to relinquish their freedom to act unilaterally.Footnote ¹²⁵ However, with the deep seabed and ocean floor having already been unanimously recognized by the UN General Assembly as a common heritage of humanity, it seems clear that under customary international law, states – including those, like the United States, that have yet to join UNCLOS – are no longer entitled to use or exploit the resources of the deep seabed and ocean floor unilaterally. Mandatory cooperation has become the universally binding legal norm.

The New Law of the Sea

Perhaps more than any other field, the law of the sea exemplifies international law’s transition from the unilateral model to the equitable model of state sovereignty. Consistent with the equitable model, UNCLOS reflects a thorough-going commitment to mandatory cooperation as a strategy for reconciling concurrent state rights, addressing unsettled boundary disputes, and managing common resources for the benefit of humanity as a whole. These features of the new law of the sea have only become further cemented through subsequent developments in international legal practice.

Recognizing mandatory cooperation’s importance to the success of the new law of the sea, in 1995 states concluded an additional agreement that further clarified how requirements to cooperate applied to the conservation and sustainable exploitation of jurisdiction-straddling and highly migratory fish stocks.Footnote ¹²⁶ Among other things, states-parties to the 1995 agreement committed to collect data necessary to facilitate effective fishery management,Footnote ¹²⁷ consult with one another “in good faith and without delay,”Footnote ¹²⁸ and “make every effort to agree on compatible conservation and management measures within a reasonable period of time.”Footnote ¹²⁹ Should agreement on conservation and management measures prove elusive, states-parties agreed that any one of them could take the resulting dispute to mandatory dispute resolution.Footnote ¹³⁰ States-parties also pledged to cooperate with one another “to enhance the ability of developing States, in particular the least-developed among them and small island developing States, to conserve and manage straddling fish stocks and highly migratory fish stocks” and “to participate in high seas fisheries for such stocks.”Footnote ¹³¹

Since the North Sea Continental Shelf Case and the Fisheries Jurisdiction Cases, the ICJ has continued to affirm that mandatory cooperation applies to the law of the sea.Footnote ¹³² Indeed, the Court has characterized mandatory cooperation as the “fundamental norm” of international maritime delimitation.Footnote ¹³³

International arbitral tribunals have also made important contributions to clarifying the requirements associated with mandatory cooperation in the law of the sea.Footnote ¹³⁴ A prominent example is the Chagos Marine Protected Area Arbitration (Mauritius v. United Kingdom).Footnote ¹³⁵ At issue in the arbitration was Mauritius’s objection to the United Kingdom unilateral declaration of a marine protected area (MPA) around the Chagos Archipelago. Mauritius argued that the proposed MPA did not reflect due regard for its legal rights as a coastal state, as required under the customary international law of the sea.Footnote ¹³⁶ The arbitral panel agreed. It explained that the United Kingdom’s obligation to give due regard to Mauritius’ rights “does not impose a uniform obligation to avoid impairment of Mauritius’ rights, nor does it uniformly permit the United Kingdom to proceed as it wishes, merely noting such rights.”Footnote ¹³⁷ Neither of those approaches was compatible with the principle of sovereign equality because each would uphold one state’s rights while effectively extinguishing the other’s rights. Respect for the equal sovereignty of both states required a more equitable, collaborative approach. The tribunal explained that the parties must take into consideration the equities involved for both sides, including the “importance [of Mauritius’s rights], the extent of the anticipated impairment, the nature and importance of the activities contemplated by the United Kingdom, and the availability of alternative approaches.”Footnote ¹³⁸ With these considerations in mind, the two states must endeavor to reconcile their respective rights through negotiation in a spirit of mutual accommodation. The United Kingdom’s failure to pursue such cooperation with Mauritius in good faith before imposing the MPA violated this customary requirement of the law of the sea.Footnote ¹³⁹ By proceeding unilaterally over Mauritius’s objections, the United Kingdom continued to treat Mauritius, its former colony, as a political subordinate rather than as an equal sovereign.

Challenges and Opportunities

As of the date of this writing, over one hundred states have signed the new High Seas Treaty,Footnote ¹⁴⁰ reaffirming their commitment to mandatory cooperationFootnote ¹⁴¹ and offering a ray of hope for marine biodiversity at a moment of great peril.Footnote ¹⁴² Yet, for every positive development like the High Seas Treaty, skeptics can point to other areas where mandatory cooperation has disappointed. For example, Arctic states have yet to resolve longstanding disputes over the Arctic Sea and the abundant resources within its continental shelf.Footnote ¹⁴³ Demanding special treatment based on historical practice, China has declined to cooperate with other states to establish by agreement maritime boundaries for the South China Sea based on equitable principles,Footnote ¹⁴⁴ and it has refused to recognize a related arbitral award from the International Tribunal for the Law of the Sea.Footnote ¹⁴⁵ States with large fishing industries often oppose reasonable limits on commercial fishing, favoring their immediate economic interests over the claims of environmental conservation and international and intergenerational equity.Footnote ¹⁴⁶ Some critics lament, therefore, that mandatory cooperation naively “assumes a degree of good will and a spirit of accommodation that is not always available among highly competitive entities.”Footnote ¹⁴⁷

However, even when states shirk their obligations of mandatory cooperation, they cannot fully escape them. For all its diplomatic and military bluster, China has not succeeded in convincing most other states, much less international courts and tribunals, to accept the legality of its unilateral claims to sovereignty over nearly all of the South China Sea.Footnote ¹⁴⁸ Arctic states recognize that their contested jurisdictional claims will not achieve general international recognition until they resolve their remaining disputes through agreement or third-party dispute resolution.Footnote ¹⁴⁹ Meanwhile, scientific cooperation has persuaded many states of the need to take aggressive collective action to prevent a massive decline in overexploited fish stocks. States that might have resisted scaling back their fishing industries a generation ago now recognize that international regulatory cooperation offers the only realistic path to restore declining fisheries for the benefit of present and future generations. While much work must still be done, the good news is that many fish stocks that were approaching depletion only a few decades ago are starting to bounce back through concerted international cooperation.Footnote ¹⁵⁰ Whether this progress can be sustained in an era of accelerating climate change and explosive population growth is an open question. If there is hope for the oceans and the human communities that depend upon them, it lies in national authorities embracing the spirit of mandatory cooperation.

An Unfinished Battle

In March 1879, Bolivian engineer Eduardo Abaroa Hidalgo found himself wounded and surrounded by the lifeless bodies of his compatriots as hundreds of hostile Chilean troops advanced toward his position. Weeks earlier, Chile invaded the Litoral, Bolivia’s arid coastal region, occupying the port city of Antofagasta and seizing control of the Atacama Desert with its lucrative nitrate deposits. Abaroa abandoned his job at a silver mine to lead the civilian resistance. As the Chilean army progressed inland, Abaroa’s men joined forces with the scanty Bolivian military presence in the region in an attempt to prevent the invaders from reaching the oasis town of Calama. After destroying two bridges across the Topáter River, Abaroa and his compatriots dug in to face the advancing army. Badly outnumbered and facing a superior force that included cavalry and heavy artillery, Abaroa’s side was quickly overwhelmed. The Bolivian military withdrew, leaving Abaroa’s volunteers to continue the fight alone until none but Abaroa remained standing. According to Bolivian lore, when the Chilean army demanded Abaroa’s surrender, his cheeky reply sealed his fate: “Me, surrender? Let your grandmother surrender, bastards!”Footnote ¹

Over a century later, Bolivia continues to commemorate the Battle of Topáter on March 23 as “The Day of the Sea” (El Día del Mar). On this national holiday, Bolivians gather to celebrate Abaroa’s heroism while also collectively mourning the loss of the Litoral and affirming their determination to regain this corridor to the Pacific. In La Paz, a casket bearing Abaroa’s remains proceeds in full ceremony of state from the Basilica of San Francisco to the Plaza Abaroa, where a monumental bronze statue honors the hero. Marching bands with majorettes, civic groups with banners, and marines clad in snow-white uniforms with polished sabers parade past the casket as the country’s president and other dignitaries look on from an elevated grandstand. Representatives of the Bolivian navy also join in the procession, proudly reaffirming their official motto: “The sea is ours by right; to take it back is our duty.”Footnote ² Meanwhile, school children throughout the country unite their voices in an anthem that every Bolivian knows by heart – the “Hymn to the Litoral” (Hymno al Litoral):

For Bolivians, reclaiming the lost Litoral is not only a matter of national pride, but also of overriding national interest. As a result of Chile’s annexation of the Litoral, Bolivia has the dubious distinction of being one of two landlocked countries in South America and one of forty-four landlocked countries worldwide.Footnote ⁴ Many of these countries became landlocked through colonial-era borders imposed by foreign powers. Unlike the developed landlocked states of Europe, the vast majority of landlocked states – including those in Africa, Central Asia, and South America – do not have navigable rivers, advanced transportation infrastructure, or a high degree of regional economic integration. As a result, they tend to experience lower economic growth than their coastal neighbors, and many rank among the most impoverished and least developed of developing countries. Bolivia, one of the poorest countries in South America, knows these disadvantages of landlocked status all too well. Thus, reclaiming the lost Litoral has dominated Bolivia’s national aspirations and foreign policy for over 140 years.

International law no longer permits states like Bolivia to shed their landlocked status by wresting territory from their neighbors through military conquest.Footnote ⁵ A landlocked state’s access to the sea therefore depends upon neighboring states enabling them to transport people and goods through their territory. In this chapter, we show how mandatory cooperation explains and clarifies the legal position of landlocked states vis-à-vis transit states. We show that international law governing landlocked states offers a classic case of conflicting entitlements under international law. On the one hand, coastal states like Chile enjoy sovereignty over their territory, including the right to “territorial integrity and political independence.”Footnote ⁶ On the other hand, landlocked states like Bolivia “have the right of access to and from the sea,” including “freedom of transit through the territory of transit States by all means of transit.”Footnote ⁷ Reconciling these conflicting entitlements is the work of mandatory cooperation.

By facilitating universal access to the sea, mandatory cooperation provides an equitable response to pathologies generated by the international legal order itself. A core function of international law is regulating the distribution of territorial sovereignty among states. The landlocked status of particular countries is the byproduct of an international legal order that validates borders established in the past through violent conquest and colonial subjugation. Absent mandatory cooperation, international law would consign landlocked states to a subservient position vis-à-vis transit states, who could arbitrarily prevent them from accessing the rest of the international community. Mandatory cooperation mitigates this structural injustice by requiring transit states to exercise their rights as territorial sovereigns in an equitable manner to facilitate foreign access to the sea.Footnote ⁸

Territorial Sovereignty or Transit Rights?

Prior to the mid-twentieth century, international publicists offered diverging viewpoints about whether the law of nations required coastal states to permit foreigners to travel through their borders. Hugo Grotius argued that all people enjoyed a legal right of innocent passage through foreign territory.Footnote ⁹ This right encompassed not only passage of persons but also goods and merchandise intended for international commerce.Footnote ¹⁰ In Grotius’s view, coastal states could not impose customs or taxes on people or goods transiting through their borders, except as reimbursement for costs incurred ensuring their security.Footnote ¹¹ Grotius considered the right to travel and trade freely to be “clear and immutable” under the law of nations.Footnote ¹²

Not everyone agreed with Grotius’s assessment. A generation later, German jurist and political philosopher Samuel Pufendorf contested Grotius’s view, arguing that under the law of nations a state was free to decide for itself how “free or cautious” it wished to be in welcoming foreigners into its territory.Footnote ¹³ According to Pufendorf, the principle of territorial sovereignty meant that “it is left in the power of all States, to take such Measures about the Admission of Strangers, as they think convenient,” subject only to a narrow exception for those “who are driven on the Coasts by Necessity, or by any Cause that deserves Pity and Compassion.”Footnote ¹⁴ Pufendorf also rejected Grotius’s view that under the law of nations “every one has a Right of trading into foreign parts” and “of importing what the People there want.”Footnote ¹⁵ Hence, “there lies no Restraint on a State, why … it should not favour its own Subjects more than Strangers … by demanding less Custom of the former, than of the latter.”Footnote ¹⁶ Although Pufendorf characterized hospitality toward foreign travelers as a morally binding “Duty of Humanity,” even this ethical obligation was subordinate to “good Reasons of State.”Footnote ¹⁷ Thus, Pufendorf believed that the nationals of landlocked states could not claim a legal entitlement to travel or transport goods through coastal states except in cases of exceptional grave necessity and “ought to rest satisfied with [whatever] Station and Privileges [a transit state deigns to] assign them.”Footnote ¹⁸

This disagreement between Grotius and Pufendorf – the two leading lights of seventeenth-century international law – cast a shadow of uncertainty over the relationship between territorial sovereignty and transit rights. Did peaceful travelers have a right to innocent passage through foreign territory? Or were coastal states free to exclude most foreign nationals?

The debate was mostly academic because coastal states in Europe tended to accept that it was in their national interest to welcome foreigners, including traders who wished to transport goods and merchandise through their borders. For example, when the Swedish empire controlled every major port on the Baltic Sea at the end of the seventeenth century, it permitted foreign merchants to travel freely and engage in commerce throughout the Baltic region, subject to modest customs duties, in order to maintain a steady flow of economic activity and tax revenue through its ports.Footnote ¹⁹ Yet Pufendorf’s vision of territorial sovereignty still spelled trouble for the commercial interests of landlocked states. By insisting that the law of nations would permit a coastal state like Sweden to close its borders to foreign traders, Pufendorf’s account threatened geographically disadvantaged states with the possibility that coastal states might eventually sever transit through their borders or impose crushing customs duties. Even when coastal states did not close their borders, the mere possibility that they might do so placed landlocked states in a vulnerable position and became a source of friction conductive to conflict.

Illustrative of this dynamic was the Great Northern War (1700–1721), when Russia allied with Denmark and Saxony to challenge Sweden’s regional hegemony. In the years leading up to the war, Tsar Peter I had made no secret of his ambition to acquire a “window to the West” by retaking territory along the Baltic that Sweden had seized from Russia nearly a century earlier in the 1617 Peace of Stolbova.Footnote ²⁰ This objective was strategically important because Russia’s access to blue water was limited to Arkhangelsk, a remote port on the White Sea to the far north. Sweden’s dominion over the Baltic coastline meant that Russia depended greatly on foreign intermediaries to deliver its commodities to foreign markets. Anxious to burnish Russia’s reputation in the West, Peter followed the conventions of European monarchs by commissioning a formal legal-historical brief to justify Russia’s intervention in the war.Footnote ²¹ Having studied keenly both Grotius’s Law of War and Peace and Pufendorf’s Law of Nature and Nations, Peter likely would have been acquainted with their divergent perspectives on transit rights.Footnote ²² It is noteworthy, therefore, that Russia’s published justification for the war cited intelligence from a Swedish prisoner of war suggesting that Sweden had been preparing to invade Russia and seize Arkhangelsk to eliminate Russia’s access to the sea and “cut off the Russians from … Commerce with Foreigners.”Footnote ²³ Although this was not Russia’s primary legal argument for entering the war, its inclusion in Russia’s war manifesto underscores Peter’s fear that Sweden might eventually invoke Pufendorf’s theory of territorial sovereignty, forbid commerce between foreigners, and establish a stranglehold on Russia’s foreign trade. The only sure way to avert this threat would be for Russia to pierce Sweden’s territorial holdings to the north and establish its own sovereign corridor to the Baltic. This plan ultimately came to fruition when Russian forces drove the Swedes from the Gulf of Finland, followed by Peter’s triumph over King Charles XII at Poltava.Footnote ²⁴ These victories enabled Peter to fulfill his dream of establishing a cosmopolitan port on the Baltic – St. Petersburg, Russia’s “Venice of the North” – which served as the opulent capital of Imperial Russia from 1703 to 1918.

For over 250 years after Poltava, the debate between Grotius and Pufendorf over transit rights continued to simmer without definitive resolution. Writing in 1904, John Westlake divided “the opinions of accredited authors” on this subject into two categories:

In the former category, Westlake placed Johan Ludwig Klüber, Georg Friedrich von Martens, August Wilhelm Heffter, Carlos Calvo, Robert Phillimore, Travers Twiss, and William Edward Hall; in the latter category, he included Grotius (obviously), Pufendorf (dubiously), Emer de Vattel, Johann Kaspar Bluntschli, F. H. Geffken, Édouard Engelhardt, and Henry Wheaton, among others.Footnote ²⁶ This debate persisted well into the twentieth century, with some commentators affirming a customary right of innocent passage and others denying the existence of such a right.Footnote ²⁷

Tensions between these competing views flared up during international negotiations in the latter half of the twentieth century, with disappointing results for landlocked states.Footnote ²⁸ In negotiations leading to the 1965 Convention on Transit Trade of Land-locked States, delegations for landlocked states argued that international law already recognized a principle of free access to the sea. Transit states did not deny the existence of such a principle of free access, but they objected that the principle was subordinate to coastal states’ territorial sovereignty.Footnote ²⁹ Unable to move beyond this impasse, the Convention affirmed that landlocked countries “should have free access to the sea,” but it did not establish a firm legal right.Footnote ³⁰ Instead, it provided that states-parties “shall by common agreement … accord: (a) [t]o the State having no sea-coast, on a basis of reciprocity, free transit through their territory,” as well as (b) “access to seaports and the use of such ports.”Footnote ³¹ Although superficially supportive of landlocked states’ interests, without according substantive legal rights to landlocked states this mere agreement to agree (pactum de contrahendo) was unenforceable under international law.Footnote ³² Ultimately, therefore, the Convention essentially codified Pufendorf’s approach to the transit interests of landlocked states: it proclaimed that coastal states and landlocked states should conclude transit agreements to facilitate oceanic access, but it did not establish a legal right to innocent passage.

Both Territorial Sovereignty and Transit Rights

Following the Convention on Transit Trade for Landlocked Countries, landlocked states continued to lobby for international recognition of a right to innocent passage to the sea. During the Third UN Conference on the Law of the Sea, landlocked states argued that their access to the sea should not depend on transit states’ consent, which was too often used as leverage to bully them during negotiations.Footnote ³³ Ultimately, transit states agreed to include a firm legal right to transit in the 1982 UN Convention on the Law of the Sea (UNCLOS).Footnote ³⁴ Article 125 of UNCLOS provides that landlocked states are entitled to exercise “the right of access to and from the sea” – including “transit through the territory of transit States by all means of transport” – so that they can enjoy the full range of rights associated with “the freedom of the high seas and the common heritage of mankind.”Footnote ³⁵

UNCLOS does not go so far as to embrace Grotius’s view that a landlocked state’s right of innocent passage trumps transit states’ territorial sovereignty. Although Article 125 establishes transit as a genuine legal right, it also affirms that transit states retain “full sovereignty over their territory.”Footnote ³⁶ Transit states therefore “have the right to take all measures necessary to ensure that the rights and facilities provided … for landlocked States shall in no way infringe their legitimate interests.”Footnote ³⁷

By affirming both a legal right to transit and the prerogatives of territorial sovereignty, UNCLOS adopts an intermediate position. Territorial sovereignty is not hierarchically superior to transit rights nor is it subordinate to transit rights. Instead, Article 125 places these entitlements in direct conflict.Footnote ³⁸ Landlocked states have a genuine legal “right” to access the sea “through the territory of transit States.” But transit states have a no less significant right to exercise “full sovereignty” in order to protect their “legitimate interests.” What emerges is a dialectic of dueling entitlements – a structural antinomy that can be reconciled only through the synthesizing praxis of mandatory cooperation.

How does UNCLOS reconcile transit states’ territorial sovereignty with landlocked states’ right to access the seas? Article 125 provides: “The terms and modalities for exercising freedom of transit shall be agreed between the land-locked States and transit States concerned through, bilateral, subregional or regional agreements.”Footnote ³⁹ Contrary to the assertion of some commentators, this requirement does not render landlocked states’ transit rights dependent on a future agreement.Footnote ⁴⁰ Article 125 is not a mere agreement to agree. Under UNCLOS, landlocked states are entitled to exercise transit rights to access the sea – full stop. But determining how this right may be exercised without undermining the transit state’s legitimate sovereign interests (e.g., public health and safety) requires international cooperation. Thus, UNCLOS contemplates that the legal entitlements of landlocked states and transit states must be reconciled harmoniously through mandatory cooperation.Footnote ⁴¹

Viewing transit rights through this lens of mandatory cooperation clarifies the legal obligations enshrined in Article 125. To satisfy their obligations to landlocked states, transit states must investigate and consult with landlocked states to fully understand and accommodate their legitimate interests with respect to the “terms and modalities for exercising freedom of transit.” They may not arbitrarily withhold – or threaten to withhold – safe passage through their territory. In this way, mandatory cooperation provides an equitable safety valve against transit states exercising their territorial sovereignty in a manner that would effectively imprison the people of landlocked states within their own national territory. Landlocked states, in turn, must respect transit states’ territorial integrity and political independence by accepting reasonable constraints on their passage through transit states. Article 125 thus places landlocked states and transit states under mutual obligations to establish cooperative frameworks for facilitating oceanic access. Failure to reach agreement about specific “terms and modalities” is not necessarily a violation of Article 125, as long as the parties remain committed to, and actively engaged in, the pursuit of an equitable solution. If negotiations reach an impasse, both sides arguably must pursue third-party dispute resolution in a good faith effort to achieve a mutually acceptable compromise that reflects due regard for their respective rights, consistent with equitable principles. Mandatory cooperation thus respects the rights of both landlocked states and transit states, while prohibiting either side from dictating unilaterally the terms of their interaction.

Bolivia v. Chile in the World Court

A recent proceeding between Bolivia and Chile in the International Court of Justice (ICJ) illustrates both the limits and promise of mandatory cooperation with regard to conflicts between landlocked and transit states. At issue in the proceeding is more than a century of diplomatic exchanges between Bolivia and Chile over the future of the disputed Litoral. For several decades after Chile’s seizure of Bolivia’s coastal region, the two countries normalized their relations through a series of agreements, while Bolivia continued to pursue a territorial outlet to the Pacific. In 1904, Bolivia and Chile concluded a Treaty of Peace and Friendship in which Bolivia formally recognized Chile’s sovereignty over its former territory in exchange for financial compensation and other concessions, but without expressly addressing Bolivia’s desire to acquire an independent corridor to the ocean.Footnote ⁴² Over the next century, Bolivia periodically renewed negotiations with Chile without success. During a temporary thaw in relations, the reigning dictator-generals of Bolivia and Chile, Hugo Banzer and Augusto Pinochet, met in 1975 at the disputed border town of Charaña to shake hands over a possible agreement to grant Bolivia a sovereign corridor to the sea.Footnote ⁴³ The tentative agreement soon unraveled under objections from both sides. The ensuing disagreement led the two countries to the brink of war in 1979, prompting Chile to plant landmines along the border. In the 2010s, Bolivia’s pretensions to the Litoral gained renewed salience as Bolivian President Evo Morales and Chilean President Sebastián Piñera each exploited the issue to stoke nationalist fervor for political gain.Footnote ⁴⁴

In 2013, Bolivia instituted proceedings against Chile in the ICJ, seeking to compel Chile to return to the negotiation table.Footnote ⁴⁵ Bolivia asserted that at various critical junctures during their diplomatic exchanges, Chile had undertaken a legal obligation to negotiate with Bolivia for the purpose of ending once and for all Bolivia’s unfortunate status as a landlocked state.Footnote ⁴⁶ Chile, however, vigorously rejected the notion that it had undertaken any such legal duty to negotiate a land surrender. Although Chile acknowledged that it had entertained Bolivian invitations to negotiate on a number of occasions, it categorically denied that its conduct reflected an intention to undertake a legal duty to negotiate with Bolivia over the possible transfer of Chilean territory to Bolivia.Footnote ⁴⁷

To be clear, in the proceedings before the ICJ, Bolivia did not assert its transit right under UNCLOS. Instead, Bolivia set its sights on a more ambitious target: securing a judgment that it was legally entitled to negotiate with Chile toward the possible return of the Litoral. Because the unilateral aspiration to acquire foreign territory is not an issue that triggers mandatory cooperation, the success of Bolivia’s strategy depended on the ICJ agreeing that Chile had, in fact, voluntarily undertaken an obligation to negotiate with Bolivia for these purposes. Had Chile undertaken such an obligation, then it would have borne a relatively modest duty to receive and consider proposals from Bolivia in good faith. Chile would not, however, have been required to endorse or give any special weight to Bolivia’s proposals. Unlike settings where mandatory cooperation applies, triggering the more robust duty of due regard, Chile would have been free to decide for itself whether, or on what terms, it would relinquish some of its coastal territory to Bolivia. Ultimately, however, the ICJ concluded that Chile had not voluntarily undertaken any such duty to negotiate with Bolivia for the purpose of granting Bolivia “sovereign access” to the Pacific.Footnote ⁴⁸ By rejecting the idea that mandatory cooperation applies to state efforts to acquire foreign territory, the ICJ’s judgment underscored the limits of mandatory cooperation as a constraint on territorial sovereignty.

Chile bears more robust duties of cooperation when it comes to facilitating transit through its territory pursuant to Article 125. Because Bolivia’s right to access the ocean under UNCLOS is in tension with Chile’s right to territorial integrity, Article 125 requires that the two states reconcile their conflicting entitlements through cooperation. Bolivia and Chile must therefore cooperate in investigating, consulting, negotiating, and, if necessary, pursuing third-party dispute resolution to establish equitable “terms and modalities” that balance their respective interests.Footnote ⁴⁹ In pursuing cooperative solutions, each state must respect the other’s legitimate interests and manifest an openness to compromise. These equitable requirements are essential not only to reconcile the states’ respective rights under international law (territorial sovereignty vs. oceanic access), but also to ameliorate historical injustices arising from Chile’s violent conquest of the Litoral and to prevent Bolivia’s landlocked status from perpetuating Chilean domination and suppressing Bolivia’s economic development.

In many respects, Bolivia and Chile have successfully implemented these legal obligations. Pursuant to the 1904 Treaty of Peace and Friendship, Chile has connected Bolivia to the Pacific by constructing and maintaining a railway line and a paved highway between Bolivia’s capitol, La Paz, and the Chilean port city of Arica.Footnote ⁵⁰ Chilean lawmakers have worked with Bolivia to reduce regulatory red tape that would otherwise impede the free flow of people and goods across Chilean territory.Footnote ⁵¹ Bolivian cargo is exempt from Chilean taxes, and Chile allows Bolivia to exercise customs powers in the Chilean city of Arica over cargo traveling to or from Bolivia.Footnote ⁵² Pursuant to agreements negotiated in 1955 and 1957, a Bolivian state-owned company operates a pipeline from Sica in Bolivia to Arica in Chile, facilitating the shipment of Bolivian oil across the high seas to markets around the world.Footnote ⁵³ To be sure, Bolivia clearly believes that further concessions by Chile are necessary – including a permanent transfer of coastal territory between the countries – to strengthen Bolivia’s political independence and boost its economic development.Footnote ⁵⁴ Yet, these lingering grievances should not overshadow the substantial progress that the states have made in reconciling their conflicting interests through diplomacy. For generations, Bolivia and Chile have managed to cooperate productively – investigating, consulting, and negotiating with one another on a wide variety of issues – in a good faith effort to balance equitably their respective sovereign interests. The fact that such a robust partnership has taken root and flourished – even as the two states remain bitterly divided over Bolivia’s aspiration to acquire a territorial corridor to the Pacific – is a testament to the promise of mandatory cooperation.Footnote ⁵⁵

Mitigating Geographic Inequity

Bolivia is not the only landlocked state that has benefited from UNCLOS’s endorsement of transit rights and mandatory cooperation. Over the past four decades, government and scholarly resistance to the legal transit rights of landlocked states has faded as 170 states have become parties to UNCLOS.Footnote ⁵⁶ Consistent with UNCLOS, transit states generally have abandoned the practice of subjecting goods in transit to customs duties and other taxes, except as remuneration for services rendered.Footnote ⁵⁷ These developments have paved the way for a host of international, regional, and bilateral agreements that facilitate oceanic access for landlocked states. International instruments such as the World Trade Organization’s Trade Facilitation Agreement have lowered customs barriers, facilitated cooperation among national transit authorities, and expedited the release and clearance of goods in transit across national borders to facilitate transit.Footnote ⁵⁸ In Africa – home to sixteen landlocked states – regional transit-facilitating agreements include the Trans-Kalahari Corridor Agreement (Botswana, Namibia, South Africa) and the African Continental Free Trade Area Agreement (thirty-two states-parties, with many more pending). After decades of tension, Somalia agreed in the recent Ankara Declaration to facilitate Ethiopia’s access to the Red Sea “within a spirit of friendship and mutual respect,” while Ethiopia recognized Somalia’s sovereign “independence and territorial integrity.”Footnote ⁵⁹ As these examples illustrate, the overall trend post-UNCLOS reflects coastal states cooperating to facilitate oceanic access for landlocked states.

International recognition of transit rights has enabled landlocked states to appeal to international organizations for assistance when disputes have arisen with their coastal neighbors. Even before UNCLOS, Lesotho successfully enlisted the assistance of the UN Security Council and UN General Assembly when Apartheid-era South Africa closed several border posts in an attempt to strong-arm its fiercely independent landlocked neighbor.Footnote ⁶⁰ In 2001, the General Assembly provided sustained institutional support for landlocked states by establishing the Office of the High Representative for the Least Developed Countries, Landlocked Developing Countries and Small Island Developing States (UN-OHRLLS). The UN-OHRLLS has worked with landlocked states and their regional neighbors to stimulate cross-border trade and transport, establish transit transport corridors, promote regional integration and infrastructure development, and facilitate integration into regional and global value chains.Footnote ⁶¹ The UN-OHRLLS has championed the Vienna Programme of Action for Landlocked Developing Countries, a ten-year cooperative global initiative (2014–2024) to promote landlocked states’ access to the sea, including by promoting regional integration, eliminating regulatory red tape, and developing essential transportation infrastructure.Footnote ⁶²

As international, regional, and bilateral cooperation has increased, landlocked states have been able to pursue economic opportunities that would have been unimaginable a half century ago. For example, in 2015 the world’s largest landlocked state, Kazakhstan, announced an audacious plan to develop a blue-water shipping fleetFootnote ⁶³ – no mean feat for a country located 3,750 kilometers from the ocean.Footnote ⁶⁴ This remarkable initiative would be impossible without the cooperation of three transit states that separate Kazakhstan from the Persian Gulf: Uzbekistan, Turkmenistan, and Iran.

Even with mandatory cooperation facilitating oceanic access, the practical disadvantages of landlocked status should not be underestimated. There are good reasons why Bolivia continues to commemorate the Day of the Sea each year, anticipating a future (real or imagined) when the lost cities of “Antofagasta, beautiful lands of Tocopilla and Mejillones next to the sea, with Cobija and Calama return to Bolivia again.”Footnote ⁶⁵ Compared to the average developing country, landlocked states like Bolivia spend more than twice as much of their export earnings on transport and insurance services.Footnote ⁶⁶ Many are at the mercy of transit delays produced by shoddy roads, bureaucratic red tape, and violent unrest in neighboring transit states. International law does not obligate transit states to construct new infrastructure to facilitate access to the sea for landlocked states. During times of port or rail congestion, coastal states may treat the needs of landlocked states as a lesser priority – particularly if they view landlocked states as competitors in the global marketplace.Footnote ⁶⁷ Due to these and other factors, the United Nations estimates that “the level of development in landlocked developing countries is on average twenty per cent lower than what it would be were they not landlocked.”Footnote ⁶⁸ Where economic development is concerned, geography is destiny.

Mandatory cooperation cannot erase the structural inequities inherent in landlocked status.Footnote ⁶⁹ However, experience has shown that international cooperation can at least mitigate the inequities of geography by enabling landlocked states to reach blue water – the gateway to international commerce.

Below the Green Waters

On June 19, 1864, an enthusiastic crowd of 15,000 spectators flocked to Cherbourg, France – some taking trains from as far away as Paris – to witness a naval duel between two celebrated adversaries from the American Civil War.Footnote ¹ Anchored in the harbor for repairs was the Alabama, the Confederacy’s most notorious and successful raider. Described by her captain, Raphael Semmes, as a model of “the most perfect symmetry” with “the lightness and grace of a swan,” the Alabama had spent the previous two years pillaging Union shipping from the Caribbean to the Cape of Good Hope to the South China Sea and back again.Footnote ² Awaiting the Alabama in the English Channel was the Kearsarge, a formidable Union warship under the command of Captain John A. Winslow. Long before the Civil War, Semmes and Winslow had cut their teeth in the US navy while serving as shipmates during the Mexican War. Their careers then followed similar trajectories: both swiftly climbed the officer ranks and received commendations for bravery before they eventually found themselves on opposite sides of the Civil War. When the Kearsarge tracked the Alabama to Cherbourg, Semmes challenged his former shipmate to battle.Footnote ³

The Alabama did not fare well in the ensuing contest. Years later, Semmes recounted what transpired in elegiac prose:

Thus ended the storied career of the Alabama, the toast of the Confederate navy.

Politicians and reporters in the Northern States preferred a less reverential epitaph for the Alabama: “British pirate.”Footnote ⁵ Three years earlier, in April 1861, an agent for the Confederacy concluded a contract with Messrs. Laird & Co. of Birkenhead, Liverpool for the construction of “a wooden-hulled ship that could be readily refitted in any port around the world, built to the highest standard of the day.”Footnote ⁶ When the US Minister to England, Charles Francis Adams, caught wind of the transaction, he urged the British government to seize the ship pursuant to the Foreign Enlistment Act of 1819, which prohibited constructing warships in British territory for a belligerent power.Footnote ⁷ To Adams’s dismay, the British Customs Office initially demurred. While recognizing that the ship in question was clearly designed for combat, the Customs Office questioned whether it had authority to intervene under domestic law when the ship as yet carried no armaments and had been commissioned nominally for a private party, not the Confederacy itself.Footnote ⁸

Union agents retained a private detective to confirm the ship’s belligerent purpose. The detective collected affidavits attesting that the Lairds were secretly recruiting British seamen with fighting experience to join the ship’s crew in support of the Confederacy.Footnote ⁹ Adams delivered these affidavits to the Customs Office in London, renewing the United States’ plea to impound the vessel. He also made arrangements for the USS Tuscarora, a Union frigate anchored in Southampton, to set course northward to intercept the warship before it could escape out to sea.

Neither of these moves succeeded. Tipped off by friends in the British government, the Lairds accelerated their plans for the warship’s departure. On July 29, 1862 – the very same day legal officers in London determined that the vessel should be detained – it slipped quietly out to sea with a skeleton crew. Two days later, customs officers in Liverpool watched passively as a tug picked up crewmembers and supplies to join the warship fifty miles away in Moelfre Bay. No effort was made to detain the ship at this rendezvous point before she pulled up anchor and departed for Terceira in the Azores, where she received her armament.Footnote ¹⁰ On August 24, 1862, Captain Semmes arrived at Terceira to assume command. Upon reading out his commission as a commander in the Confederate navy, Semmes raised the Confederate flag and christened the ship the CSS Alabama.Footnote ¹¹

Over the next two years, the Alabama traveled 75,000 miles, a distance roughly equivalent to circling the world three times.Footnote ¹² Along the way, it captured and destroyed dozens of Union ships, causing losses in the millions of dollars, and planting fear in the hearts of merchants and seamen around the world.Footnote ¹³ In 1863 Adams wrote in protest to UK Foreign Secretary Earl Russell. The United States, he wrote:

Adams stressed that the Alabama had been constructed on British soil by British subjects and operated by a British crew with the express purpose to make war against the United States.Footnote ¹⁵ In Adams’s view, these considerations meant that the British government was “bound by treaty obligations and by the law of nations to prevent” the Alabama from leaving port. Having neglected that responsibility time and again, the British government was obligated under the law of nations to compensate “the peaceful lawabiding citizens of the United States” for the Alabama’s ruinous “depredations.”Footnote ¹⁶

The US government continued to press these claims after the war. In an 1869 speech, Senator Charles Sumner of Massachusetts castigated the United Kingdom for its ties to the Alabama. Particularly maddening, Sumner noted, was how the United Kingdom had welcomed the Alabama with open arms whenever she sailed around the world:

Given the United Kingdom’s failure to prevent the Alabama from preying on Union shipping, the consequences under the law of nations were clear: the British government “must respond in damages,” Sumner declared, furnishing compensation “not only to the individuals who have suffered but also to the National Government, acting as paterfamilias for the common good of all the people.”Footnote ¹⁸

The two states eventually agreed to submit the Alabama controversy to arbitration.Footnote ¹⁹ In the Treaty of Washington of 1871, they stipulated to several rules that would govern the tribunal’s decision. First, a neutral state, such as the United Kingdom, must “use due diligence to prevent the fitting out, arming, or equipping, within its jurisdiction, of any vessel which it has a reasonable ground to believe is intended to … carry on a war against a Power with which it is at Peace,” as well as to prevent any such vessel from escaping its jurisdiction.Footnote ²⁰ Second, a neutral state may not allow belligerents to use its ports or waters as a safe harbor for recruiting, restocking, or launching attacks. And third, a neutral state must “exercise due diligence in its own ports and waters, and, as to all persons within its jurisdiction, to prevent any violation of the foregoing obligations.”Footnote ²¹ The United Kingdom resisted characterizing these rules as customary international law, but it agreed to accept them for the Alabama controversy in the interest of nurturing “friendly relations between the two countries.”Footnote ²²

In the proceedings that followed, the British government asserted that it had practiced due diligence by enforcing its Foreign Enlistment Act in good faith. The arbitral tribunal disagreed. On September 14, 1872, the tribunal issued a decision and award that endorsed the United States’ position that due diligence required a higher level of vigilance commensurate with the serious threat the Alabama posed to the United States.Footnote ²³ The tribunal concluded that the British government had not acted on the United States’ pleas for assistance with “all possible solicitude.”Footnote ²⁴ In particular, the government failed “to take in due time any effective measures of prevention,” and “those orders which it did give at last, for the detention of the vessel, were issued so late that their execution was not practicable.”Footnote ²⁵ These belated half-measures did not reflect due diligence. Accordingly, the tribunal concluded that the United Kingdom was liable to the United States for millions of dollars in commercial losses inflicted by the Alabama.Footnote ²⁶

Before long, the standards of state responsibility applied in the Alabama arbitration achieved wider acceptance as general international law. In 1875, the influential Institute de Droit International endorsed the rules applied in the arbitration.Footnote ²⁷ States later accepted the rules in the Hague Convention of October 18, 1907:

As long as states remained neutral with respect to foreign wars, they were required to prevent their territory from being used as a staging ground for transboundary attacks. The Alabama controversy thus became a path-breaking precedent for the principle that states must exercise due diligence to prevent violent actors from using their territory to inflict significant harm abroad.

Taking the Alabama controversy as a point of departure, this chapter explores a variety of settings where international law obligates states to cooperate with one another to suppress harm caused by dangerous non-state actors, such as pirates, terrorists, and computer hackers. Since the Alabama dispute, the international community has recognized that international law requires states to exercise due diligence to prevent criminals in their territory from causing significant injuries to foreign states and foreign nationals. Only more recently, however, has the international community embraced the idea that states also bear legal obligations to cooperate with one another to suppress such transnational crimes. Nonetheless, this chapter shows that mandatory cooperation has now become firmly embedded in multilateral conventions on piracy and terrorism. Mandatory cooperation is also beginning to gain traction in international law governing cyberattacks, though the framework is embryonic.

From Due Diligence to Mandatory Cooperation

Following the Alabama arbitration, domestic courts and international tribunals extended the due diligence standard to a variety of other contexts where non-state actors threatened to inflict serious harm on foreign states or foreign nationals. For example, in the 1887 case United States v. Arjona, the US Supreme Court declared that this standard applied to currency counterfeiting:

Quoting Vattel, the Court explained that if a state “allows and protects false coiners who [counterfeit foreign currency], she does that nation an injury.”Footnote ³⁰ Thus, the law of nations obligated the United States to exercise due diligence to prevent and criminalize counterfeiting, as well as to prosecute false coiners.Footnote ³¹

International tribunals also have applied the due diligence standard to other transnational crimes. For example, following the assassination of an Italian general and other officials in Greece, a Commission of Jurists appointed by the League of Nations affirmed that a state is responsible for injuries to foreigners if it does not take “all reasonable measures for the prevention of the crime” and for bringing the perpetrators to justice.Footnote ³² By 1927, when the Permanent Court of International Justice (PCIJ) decided the landmark Lotus Case, Judge John Bassett Moore confidently observed that it was “well settled that a state is bound to use due diligence to prevent the commission within its dominion of criminal acts against another nation or its people.”Footnote ³³ The ICJ would endorse this principle later in the Corfu Channel CaseFootnote ³⁴ and the Tehran Hostages Case.Footnote ³⁵ In sum, states are obligated under international law to exercise due diligence in preventing criminal activities within their jurisdiction from inflicting significant harm on foreign states or foreign nationals.

But what precisely does “due diligence” demand of states? Some requirements are uncontroversial. At a minimum, states where criminal activities originate must take reasonable steps to prevent and suppress transnational harm. They must investigate crimes to determine the nature and extent of the threats, and they must make a reasonable effort to disrupt criminal behavior through law enforcement and prosecution. These basic requirements stem from the general customary obligation to prevent significant transboundary harm.

In principle, due diligence should also require international cooperation, because states often cannot respond effectively to transnational crime without foreign assistance. The Alabama affair illustrates this dynamic. Recall that it was American agents who first tipped off the British government that the Alabama was destined for the Confederacy. Given the gravity of the threat, the British government should have undertaken a more diligent investigation of the warship. Once the British government confirmed the Alabama’s belligerent purpose, it should have exchanged information and cooperated with Union officials to ensure that the Alabama could not slip away to inflict harm abroad. If that failed, the British government should have detained the Alabama when it later sought safe harbor in colonial ports while inviting assistance from the United States to gather evidence necessary to prosecute the Alabama’s British crew. By withholding its cooperation at each of these stages, the British government defaulted on its legal obligation to diligently prevent and suppress transboundary attacks.

International law today supports the idea that at least some transnational crimes trigger mandatory cooperation. States from which transnational crime originates must exchange information, consult, and negotiate with states that are likely to suffer injury in order to ensure that their laws, policies, and practices are adequate to avert the anticipated harm. When disagreements arise, states must resolve their differences through negotiation or third-party dispute resolution. Without such cooperation, states that serve as hosts for transnational crime would be complicit in the wrongs inflicted on other states and foreign nationals, ultimately undermining the principle of sovereign equality. Respect for sovereign equality favors applying mandatory cooperation to all significant transnational boundary harms, including criminal activities that adversely impact foreign states and foreign nationals.

Joining Forces to Stop Piracy

International law now unequivocally requires mandatory cooperation to suppress piracy. Few international norms have a longer historical pedigree than the prohibition of piracy. For centuries, international lawyers have characterized pirates as “enemies of all mankind” (hostis humani generis) – outlaws whom all states are authorized to subdue for humanity’s benefit.Footnote ³⁶ Conventional wisdom suggests that all states have an interest in suppressing piracy, so states have strong incentives to cooperate for this purpose. Only relatively recently, however, has international law generated affirmative obligations for states to cooperate in combatting pirate attacks.

An important first step in this direction is the 1982 UN Convention on the Law of the Sea (UNCLOS), which endorses mandatory cooperation in significant respects by declaring that states must “cooperate to the fullest possible extent in the repression of piracy.” However, UNCLOS defines “piracy” to include only acts of violence, detention, or depredation that take place “on the high seas” or “in a place outside the jurisdiction of any State.”Footnote ³⁷ Attacks that take place in port or within a state’s internal waters or territorial sea might be punishable under domestic law, but they do not qualify as “piracy” under UNCLOS. Hence, mandatory cooperation extends only to acts committed outside states’ exclusive territorial jurisdiction.Footnote ³⁸ UNCLOS thus neglects the most promising opportunities for suppressing piracy – before pirates reach open sea.Footnote ³⁹

These geographic limits on mandatory cooperation might have become permanent had the international community not been shocked into action a few years later by a horrific incident in the Mediterranean Sea. In 1985, four members of the Palestinian Liberation Front (PLF) forcibly boarded an Italian passenger liner, the Achille Lauro, which had put into port in Alexandria, Egypt. The hijackers forced the captain to depart with twelve passengers held at gunpoint. Among the hostages was Leon Kinghoffer, a disabled sixty-nine-year-old. When the hijackers’ demands were not met, the gunmen “pushed Klinghoffer’s wheelchair to the edge of the deck, shot him in the back, and pitched his still-twitching body into the sea.”Footnote ⁴⁰

Following the Achille Lauro incident, an overwhelming majority of states agreed to pursue more robust collaboration in the 1988 Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation (SUA Convention).Footnote ⁴¹ The SUA Convention requires states-parties to criminalize and punish certain acts, such as seizing a ship by force, destroying a ship, and killing or injuring people aboard a ship in the course of such activities.Footnote ⁴² States-parties also must “afford one another the greatest measure of assistance in connection with … criminal proceedings,” including through rendering assistance in obtaining evidence for criminal prosecution.Footnote ⁴³ The SUA Convention also promotes international cooperation by creating an independent mechanism to facilitate extradition.Footnote ⁴⁴ Most important for present purposes, states-parties agree to cooperate with one another in preventing piracy and terrorism at sea, including by employing “all practical measures to prevent preparations in their respective territories for the commission of those offenses,” as well as by exchanging information and “co-ordinating administrative and other measures … to prevent the commission of offenses.”Footnote ⁴⁵ The SUA Convention therefore brings mandatory cooperation home by requiring states to cooperate with one another to prevent and suppress piracy at its source – within their own national jurisdictions. And when disputes arise that cannot be resolved through negotiation, states-parties may take cooperation to another level by initiating binding arbitration or adjudication in the ICJ.Footnote ⁴⁶

Among the maritime spaces most vulnerable to pirate attacks are the Straits of Malacca and Singapore. The distinctive geographic features and human uses of these straits make them a congenial setting for piracy. Dividing Indonesia, Malaysia, and Singapore for 520 nautical miles, the Straits of Malacca and Singapore are strategically important highways for shipping to and from some of the world’s busiest ports, including Hong Kong, Jakarta, Pusan, Shanghai, Singapore, and Tokyo. Narrow and crowded with small fishing craft and commercial vessels traveling at low speeds, the straits offer abundant opportunities for pirates to launch quietly from the coasts, blend into the bustling maritime traffic, strike targets quickly, and then disappear into hidden retreats along the shoreline. As a result of these factors, piracy became a serious problem in the region at the end of the 1990s and in the early 2000s. The vast majority of attacks in the straits did not technically qualify as “piracy” under the terms of UNCLOS, because they occurred within the territorial waters of Indonesia, Malaysia, or Singapore.Footnote ⁴⁷ To make matters worse for user states, Indonesia, Malaysia, and Singapore resisted overtures to establish international counter-piracy patrols in the straits on the grounds that the straits were within their exclusive sovereign jurisdiction.Footnote ⁴⁸

Despite this hesitation, Indonesia, Malaysia, and Singapore have made important strides in preventing and suppressing piracy and armed robbery in the straits, and they have embraced multilateral cooperation by working with user states to strengthen their capacities to combat piracy. In July 2004, the three states began conducting joint naval patrols. Later the same year, they joined the Association of Southeast Asian Nations (ASEAN) sister-states and six other Southeast Asian states to conclude a Regional Agreement on Combatting Piracy and Armed Robbery Against Ships in Asia (ReCAAP). This agreement provides for information sharing, collaborative capacity building, and cooperative enforcement among the states parties.Footnote ⁴⁹ In September 2005, the International Maritime Organization (IMO) also convened a meeting of littoral and user states in Jakarta to address piracy. The meeting produced a joint-statement that emphasized “the need to balance the interest of the littoral States and the user States while respecting the littoral States’ sovereignty, and to establish a mechanism to facilitate cooperation between them to discuss issues relating to the safety, security and environmental protection of the Straits of Malacca and Singapore, including exploring possible options for burden sharing.”Footnote ⁵⁰ Other multilateral initiatives have generated an Information Sharing Centre in Singapore and a formal Cooperative Mechanism consisting of three components: a Cooperation Forum, a Project Coordination Committee, and an Aids to Navigation Fund.Footnote ⁵¹ Working through the Cooperation Mechanism, littoral states have accepted valuable training and technology, such as surface search radars, from user states to assist them in their counter-piracy efforts. By the time Indonesia, Malaysia, and Singapore invited Thailand to join their regional counter-piracy patrols in 2008 under the renamed Malacca Straits Patrols, piracy in the straits had dropped precipitously, from 187 incidents in 2003 to 65 in 2008.Footnote ⁵² International lawyers and security experts have hailed cooperation in the Straits of Malacca and Singapore as “the great counter-piracy success story.”Footnote ⁵³

Piracy off the Horn of Africa presents different challenges. Like the Straits of Malacca and Singapore, the Horn of Africa is a major crossroads for international shipping, with 33,000 ships transiting through the nearby Gulf of Aden each year.Footnote ⁵⁴ However, when piracy exploded around the Horn of Africa in the early 2000s, it reflected a distinct set of social, political, and economic dynamics. Particularly salient were government fragility in Puntland, the region of Somalia where most piracy in the region originates, and the limited law enforcement capabilities of other coastal states in East Africa.Footnote ⁵⁵ Whereas coastal states have been willing to take the lead in combatting pirate attacks and armed robbery around the Straits of Malacca and Singapore, Somalia has been unable to shoulder this responsibility along its lengthy 2,000-mile shoreline.

This resulting governance gap off the coast of Somalia has been ameliorated through international cooperation. In 2008, the UN Security Council determined that piracy and armed robbery off the coast of Somalia constituted a threat to international peace and security in the region.Footnote ⁵⁶ Invoking its binding authority under Chapter VII of the UN Charter, the Security Council urged states to cooperate with one another and with relevant international organizations to share information about Somali pirate attacks and render assistance to threatened vessels. It also called upon states to assist in enhancing the capacities of Somalia and other coastal states to combat piracy. And it authorized user states to enter and perform law enforcement functions within Somali territorial waters, in cooperation with the Somali government, to suppress piracy and armed robbery.Footnote ⁵⁷ Significantly, the Security Council explained that these measures should not be construed as impinging on Somalia’s territorial sovereignty because Somalia’s central government had consented to the measures. The Security Council also cautioned that the measures thus established were context-specific, in the sense that they “shall not be considered as establishing customary international law” authorizing international intervention to suppress piracy elsewhere.Footnote ⁵⁸

The Security Council’s efforts to promote international cooperation have inspired a wide variety of counter-piracy missions, cooperative agreements, and informal networks for safeguarding shipping off the Horn of Africa. Prominent examples including the Combined Task Force 151 (CTF-151), which involved ships from twenty-five participating countries, and NATO’s “Operation Ocean Shield,” which provides naval escorts and general deterrence patrols in the region.Footnote ⁵⁹ The African Union has incorporated regional cooperation against piracy into its 2050 Integrated Maritime StrategyFootnote ⁶⁰ and the African Charter on Maritime Security and Safety and Development in Africa (Lomé Charter).Footnote ⁶¹ Thanks in part to these diverse commitments and institutional arrangements for cooperation,Footnote ⁶² piracy around the Horn of Africa has plummeted since its peak in the early 2000s.Footnote ⁶³

In sum, the past twenty years have witnessed a remarkable turn toward multilateral cooperation for combatting piracy. The overwhelming majority of states have committed by treaty to assist one another in preventing and suppressing piracy not only outside their jurisdiction (UNCLOS) but also within their jurisdiction (SUA Convention). Coastal states must, at a minimum, consult and exchange information about piracy with other interested states. They must also work with other states to improve their capacity to prevent pirates in their waters from launching attacks on foreign vessels. When coastal states are incapable of preventing such attacks, due diligence requires that they pursue international cooperation, either by accepting training and resources from other states and international organizations to bolster their national anti-piracy efforts (as in the Straits of Malacca and Singapore) or by allowing user states or international organizations to undertake law enforcement operations within their territorial waters (as in Somalia).Footnote ⁶⁴ All of these requirements can be understood as corollaries of the Alabama doctrine that states must exercise due diligence to prevent their territories from being used as staging grounds for attacks on foreign states and foreign nationals.

Countering Terrorism

Mandatory cooperation also features centrally in the international law of counterterrorism. The UN General Assembly expressly embraced mandatory cooperation in its 1994 Declaration on Measures to Eliminate International Terrorism.Footnote ⁶⁵ The Declaration affirms that states bear “obligations under the Charter of the United Nations and other provisions of international law with respect to combatting international terrorism,” including the duty to “ensure that their respective territories are not used … for the preparation or organization of terrorist acts … against other States or their citizens.”Footnote ⁶⁶ More important for present purposes, the Declaration proclaims that states must “cooperate with one another in exchanging relevant information” and “endeavour to conclude special agreements [to prevent and suppress terrorism] on a bilateral, regional and multilateral basis.”Footnote ⁶⁷ The Declaration thus envisions states as bearing affirmative obligations under the Charter and customary international law to promote international peace and security through coordinated counterterrorism.

By making the case for mandatory cooperation, the General Assembly paved the way for a series of multilateral treaties that required international cooperation against terrorism. Within a few years, states concluded the International Convention for the Suppression of Terrorist BombingsFootnote ⁶⁸ and the International Convention for the Suppression of the Financing of Terrorism.Footnote ⁶⁹ Both agreements committed states parties to “afford one another the greatest measure of assistance in connection with criminal investigations or criminal or extradition proceedings,” as well as to “cooperate in the prevention of [terrorism] … by exchanging accurate and verified information … to prevent the commission of [terrorist] offences.”Footnote ⁷⁰ The 2005 International Convention for the Suppression of Acts of Nuclear Terrorism (Nuclear Terrorism Convention) also requires states to cooperate by exchanging information, consulting and assisting one another in the investigation and prosecution of terrorists, and resolving disputes through negotiation or arbitration.Footnote ⁷¹ The Nuclear Terrorism Convention underscores that states must discharge these cooperative obligations “in a manner consistent with the principles of sovereign equality,” “territorial integrity,” and “non-intervention in the domestic affairs of other States.”Footnote ⁷²

The UN Security Council has also endorsed mandatory cooperation in this field. Security Council resolutions direct states to assist one another with counter-terrorism efforts by exchanging information, collaborating to apprehend and prosecute suspects, and working together to disrupt suspects’ travel, communications, and financing.Footnote ⁷³ The Security Council has also “call[ed] upon all States to become party, as a matter of urgency, to the international counter-terrorism conventions,” including the Nuclear Terrorism Convention specifically.Footnote ⁷⁴ Through these and other directives, the Security Council has played an important role in coordinating international efforts to prevent, suppress, and punish terrorist attacks.

International cooperation against terrorism, however, has a notorious dark side. Following the 9/11 terrorist attacks, the United States collaborated with foreign partners to bring about the enforced disappearance, prolonged arbitrary detention, torture, and cruel, inhuman, and degrading treatment of suspected terrorists.Footnote ⁷⁵ The Security Council has also courted controversy by directing states to freeze the assets of terrorist suspects without affording them due process of law.Footnote ⁷⁶ These striking abuses offer stark reminders that mandatory cooperation can be turned to pernicious ends and that safeguards are necessary to help ensure that cooperation is practiced consistent with states’ other obligations under international law – including international human rights law.

Curiously, international lawyers generally give short shrift to mandatory cooperation as an emergent feature of international counter-terrorism law. When discussing transnational counter-terrorism, legal scholars and practitioners tend to focus on the options for unilateral state action. In particular, international lawyers have debated whether a state exposed to transboundary terrorist attacks (the target state) may use force against terrorists abroad without the consent of the state where terrorists are located (the host state). The ICJ has intervened in this debate by holding that the UN Charter does not allow a target state to use force in self-defense unless attacks from nonstate actors are imputable to the host state.Footnote ⁷⁷ Some commentators contest the ICJ’s position, arguing that international law permits states to use force abroad without a host state’s consent if the host state is “unwilling or unable” to eliminate the threat.Footnote ⁷⁸ What makes this debate so challenging is that the two dueling approaches share a common defect: taken at face value, they would both undermine the principle of sovereign equality. By narrowly defining the right of self-defense, the ICJ’s approach would make a target state powerless to protect its people when a host state is unwilling or unable to eliminate transboundary attacks. This would exalt the host state’s territorial sovereignty at the expense of the target state’s right to territorial integrity. But the “unwilling or unable” theory of unilateral self-defense is no better, when considered from a sovereign equality perspective, because it would subordinate the host state’s territorial sovereignty to the target state’s security demands. Whichever path one chooses, the result is similar: one state is entitled to exercise sovereign rights, while the other is not. Transnational counter-terrorism becomes a zero-sum game that subverts the principle of sovereign equality.

Mandatory cooperation suggests a better way forward. As previous chapters have shown, it is possible to reconcile territorial sovereignty with territorial integrity, but only if states cooperate with each other in accordance with equitable principles. To respect the principle of sovereign equality, host states must refrain from invoking their territorial sovereignty as a basis for refusing to assist with preventing and suppressing terrorism. To shirk this obligation would constitute an abuse of right. Nor may target states invoke their “inherent right to self-defense”Footnote ⁷⁹ as a justification for conducting unauthorized cross-border interventions in violation of host states’ territorial sovereignty; this, too, would be an abuse of right.Footnote ⁸⁰ Instead, international law obligates states to cooperate in developing equitable, negotiated solutions for confronting transnational terrorism.

When a host state is unable to prevent transboundary attacks on its own, counterterrorism can take a page from the law and practice of counter-piracy. In both settings, there are at least two options for reconciling territorial sovereignty with territorial integrity. First, the host state may enlist international assistance to enhance its capacity for effective law enforcement (as in the Straits of Malacca and Singapore). Second, it may authorize other states to perform selective law enforcement functions within its territory (as at the Horn of Africa). Both options offer practical solutions for combatting terrorism without sacrificing sovereign equality. General principles of mandatory cooperation suggest that the choice between these options should be made through international consultation and negotiation between interested states or, if necessary, by an authoritative international body like the Security Council.

Obstacles to Mandatory Cooperation against Cybercrime

Although mandatory cooperation has made substantial inroads into the law of piracy and terrorism, the same cannot be said for many other transnational crimes.Footnote ⁸¹ In the digitally networked world of the twenty-first century, failures of international cooperation have become especially problematic with regard to transboundary cyberattacks, such as computer hacking, malware attacks, and distributed denial of service (DDOS) attacks.Footnote ⁸² Malware attacks launched from one country can easily reverberate around the world, wreaking havoc in many countries. Hackers have deployed transboundary cyberattacks to obtain illicit profit, advance political agendas, or simply for sport.Footnote ⁸³ The global harm inflicted by cybercriminals has reached staggering proportions and increases every year. Experts estimate that in 2025 cybercrime cost the world approximately USD 10.5 trillion.Footnote ⁸⁴ Yet, international lawyers have been slow to embrace the idea that states bear obligations under general international law to cooperate with one another for the purpose of combating cybercrime.

Cyber security vaulted to the top of the international community’s agenda in April 2007, when a tsunami of debilitating cyberattacks struck Estonia. Reacting to the Estonian government’s decision to relocate a controversial World War II monument, the Bronze Soldier, hackers in various countries, including Egypt, Peru, and (principally) Russia, overwhelmed Estonia’s cyber-infrastructure with DDOS attacks and other mischief. These attacks paralyzed the office of the Estonian president and key government ministries, as well as banks, newspapers, television stations, and schools.Footnote ⁸⁵ More than two weeks passed, with Estonia teetering on the brink of “a complete digital collapse,” before the country’s Cyber Emergency Response Team finally managed to turn the tide.Footnote ⁸⁶

In the years following Estonia’s cyber siege, legal experts have gathered periodically in Tallinn to clarify and systematize the international law of cyberattacks. These consultations have produced an influential restatement of the law: the Tallinn Manual on the International Law Applicable to Cyber Operations, now in its second edition.Footnote ⁸⁷ The Tallinn Manual affirms that “[a] State must exercise due diligence in not allowing its territory, or territory under its governmental control, to be used for cyber operations that affect the rights of, and produce serious adverse consequences for, other States.”Footnote ⁸⁸ The International Group of Experts (IGE), who prepared the Tallinn Manual, agreed unanimously that the requirement to exercise due diligence in combatting transboundary attacks “is a general principle that has been particularized in specialized regimes of international law” and “applies in the cyber context.”Footnote ⁸⁹ Hence, states must “take all measures that are feasible in the circumstances to put an end to cyber operations that affect a right of, and produce serious adverse consequences for, other States.”Footnote ⁹⁰ However, the IGE declined to follow this due diligence requirement to its logical conclusion by affirming that states must cooperate with one another to ensure that their efforts to suppress cyberattacks are effective. According to the IGE, “customary international law does not generally oblige States to cooperate with other States in domestic criminal law matters … even if such matters have a transnational character.”Footnote ⁹¹ Absent a treaty-based requirement or other specific legal obligation, “States are not obliged to cooperate in the investigation and prosecution of cyber crime.”Footnote ⁹² Given the Tallinn Manual’s status as the leading reference on the international law of cyberattacks, many international lawyers would consider mandatory cooperation against cyber crime to be a welcome proposal for the law’s future development (lex ferenda) but not an accurate description of the law as it exists today (lex lata).Footnote ⁹³

Even if customary international law has yet to incorporate mandatory cooperation against cyberattacks, cooperation has become obligatory for states that have joined the Council of Europe’s Convention on Cybercrime, better known as the Budapest Convention.Footnote ⁹⁴ With sixty-seven states-parties, including Australia, Israel, Japan, Nigeria, the United States, and dozens of European states, the Budapest Convention reflects a growing recognition among states “that an effective fight against cybercrime requires increased, rapid and well-functioning international co-operation in criminal matters.”Footnote ⁹⁵ To this end, the Convention not only criminalizes cyberattacks and requires states parties to prevent attacks from their territories, but also obligates states parties to “cooperate with each other … to the widest extent possible for the purposes of investigations or proceedings concerning criminal offences related to computer systems and data, or for the collection of evidence in electronic form of a criminal offence.”Footnote ⁹⁶ States parties to the Budapest Convention also agree to “consult periodically” with each other with a view to facilitating “the effective use and implementation of the Convention” and “the exchange of information on significant legal, policy or technological developments pertaining to cybercrime and the collection of evidence.”Footnote ⁹⁷ Disputes over the interpretation or application of the Convention are to be resolved cooperatively through negotiation or third-party dispute resolution.Footnote ⁹⁸

A notable weakness of the Budapest Convention is its failure to gain the support of chronic offenders like China, North Korea, and Russia. Observers speculate that one reason why these states have not joined the Convention is that they are reluctant to cooperate with the international community in investigating malicious cyber activities conducted by their nationals and other users of their digital infrastructure.Footnote ⁹⁹ Further complicating the deepening East/West cyber rivalry are philosophical differences over the possible goals of international cooperation. Within the past decade, China, Kazakhstan, Kyrgyzstan, Russia, Tajikistan, and Uzbekistan have proposed an alternative to the Budapest Convention: a draft International Code of Conduct for Information Security.Footnote ¹⁰⁰ Western officials have criticized the Code for focusing exclusively on terrorism and other online content that “might contribute to political instability and regime change” to the exclusion of conventional cybercrimes, such as political and economic cyberespionage, malware attacks, and DDOS attacks.Footnote ¹⁰¹ The Code does call for mandatory cooperation, but principally in the service of suppressing domestic political dissent.Footnote ¹⁰² These features have made the proposed Code anathema to liberal democracies. In the near term, therefore, the prospects are not promising for mandatory cooperation to become customary international law for cyberattacks; as long as the world’s major powers cannot agree about what kinds of online activities require prevention and suppression, mandatory cooperation will struggle to gain a firm foothold in general international law.

Mandatory Cooperation as Global Governance

A common feature of the transnational crimes discussed in this chapter – piracy, terrorism, and cyberattacks – is that they all depend on states for further specification and enforcement. Unlike international crimes, such as genocide and crimes against humanity, which are defined by treaty and fall within the jurisdiction of international criminal tribunals, states are expected to take the lead in criminalizing, investigating, and prosecuting transnational crimes. Therefore, transnational criminal law might seem to embrace decentralization as an alternative to multilateral governance.Footnote ¹⁰³

As this chapter has shown, however, the decentralized features of transnational criminal law are paired with a complementary practice: mandatory cooperation. International treaties codify obligations to cooperate in combatting transnational crimes, including by exchanging information, sharing resources and expertise, consulting on matters of common concern, and resolving disputes through negotiation or third-party dispute resolution.Footnote ¹⁰⁴ These aspects of mandatory cooperation complement the otherwise decentralized structure of transnational criminal law, providing a framework that enables states to address transnational crime collectively while respecting sovereign equality.

Ashes of Death

When the Japanese fishing craft Lucky Dragon (Fukuryu Maru) reached Tokyo Bay on March 14, 1954, the entire crew and 4,000 pounds of tuna onboard were dangerously radioactive. Two weeks earlier, the United States had conducted the first detonation of a hydrogen bomb at Bikini Atoll in the Marshall Islands, deep in the South Pacific.Footnote ¹ The US Atomic Energy Commission (AEC) had previously announced plans to use the islands as a testing ground for nuclear weapons, and it had advised foreign governments to keep ships outside a 50,000-square-mile “danger area” for their safety. This designated danger area proved to be woefully inadequate. The magnitude of the hydrogen bomb’s thermonuclear explosion more than doubled scientific projections, and due to an unforeseen shift in atmospheric conditions, the resulting radiation cloud traveled outside the official danger area to drop a “ghostly white rain, thick with ash” on the Lucky Dragon.Footnote ² When the rain subsided, crew members experienced dizziness, vomiting, and fever – the first visible symptoms of severe radiation exposure. By the time the Lucky Dragon returned to Japan, most of the crew suffered from headaches, skin burns, bleeding gums, and other afflictions.Footnote ³ Six months later, crew member Aikitchi Kuboyama died, and twenty-two others continued to receive hospital treatment for serious injuries.Footnote ⁴ Reflecting on Kuboyama’s untimely passing, a Japanese newspaper inquired, “Has the death of a citizen ever been watched by so many eyes? They are the eyes of a strong anger and protest against the ‘ashes of death.’”Footnote ⁵

The botched nuclear test at Bikini Atoll was among the first in a series of highly publicized environmental disasters that fixed the world’s attention on the growing threat of transboundary pollution. In 1967, the Torrey Canyon, an American-owned and chartered tanker manned by an Italian crew, attracted international infamy when it ran aground on the Seven Stones reef in international waters. Approximately 80,000 tons of crude oil spilled into the Atlantic, befouling resort beaches and decimating sea bird populations along the coast of Cornwall, England.Footnote ⁶ A decade later, another oil spill eclipsed the Torrey Canyon incident when the Amico Cadiz, an American-owned supertanker, collided with a submerged reef and broke in half, dropping nearly all of its 230,000-ton load of crude oil to contaminate the French coastline for hundreds of miles. The year 1986 brought two environmental calamities in quick succession: the Chernobyl nuclear meltdown near Kyiv, Ukraine, which scattered its own “ashes of death” and eventually radiation throughout Europe, and the Sandoz chemical plant fire in Switzerland that sent thousands of liters of highly toxic pesticides down the Rhine to poison wildlife and drinking water in Germany, France, and the Netherlands. In each of these incidents, pollution from one state traversed international borders to inflict grave harm.

Like international disputes over the apportionment of watercourses and fisheries, transboundary pollution presents a classic clash of sovereign entitlements. On the one hand, international law gives states sovereign authority over activities within their territorial jurisdiction – including activities that produce pollution. But on the other hand, international law also entitles states to territorial integrity.Footnote ⁷ This means states are entitled to demand the cessation of transboundary pollution that causes significant harm within their borders.Footnote ⁸

The unilateralist theory of sovereignty would resolve this tension, for all intents and purposes, in favor of the state where transboundary pollution originates. Recall that under the unilateralist theory, states may decide how to exercise their sovereign powers without regard to foreign interests. Accordingly, the unilateralist theory would empower states to engage in practices, such as atmospheric nuclear testing, that generate harmful transboundary pollution. The unilateralist theory would threaten to render illusory the sovereign right to territorial integrity because the enjoyment of the right would depend on the mercy or grace of other states. The “no significant harm” principle from international environmental law would be subordinated to the originating state’s discretion. In an international legal order based on unilateral sovereignty, strong states would be free to do as they please within their borders, while weak states would “suffer what they must.”Footnote ⁹

International environmental law rejects this vision of sovereign unilateralism, embracing an equitable approach that respects and reconciles states’ sovereign interests. Although states have exclusive authority to regulate pollution within their borders, international law requires them to exercise this authority in a manner congenial to other states’ territorial integrity. The primary mechanism for achieving this reconciliation is the requirement that states must exercise due diligence to prevent activities in their territory from producing significant transboundary harm.

This chapter shows how due diligence leads to mandatory cooperation. To satisfy the due diligence standard, states must take into account foreign interests when they regulate activities that may produce transboundary harm. Due diligence also imposes procedural obligations to conduct environmental impact assessments, provide notice to states that may be impacted by transboundary pollution, engage in meaningful consultation and negotiation, and resolve disputes through mediation, arbitration, adjudication, or other third-party dispute resolution. The requirements of mandatory cooperation thus apply to transboundary pollution under international law.

Good Neighbors

Less than ten miles north of the Canada-US border lies Trail, a modest mining town in British Columbia. For over a century, Trail has hosted the world’s largest zinc and lead smelter, a sprawling complex adjacent to the Columbia River. Celebrated as “the jewel of the British Columbian mining industry,” the Trail smelter has served as a “locus of regional growth, a pillar of provincial development, and an instrument of Canadian economic policy.”Footnote ¹⁰ For environmentalists and international lawyers, Trail has also become synonymous with industrial pollution. In the late 1920s, the Trail smelter provoked international controversy when it became apparent that the sulfur dioxide fumes emitted in prodigious quantities from its 409-foot smokestack were devastating timber lots, orchards, gardens, pastures, and farmland in neighboring Washington State.Footnote ¹¹ Aggrieved American homesteaders demanded that the smelter cut back its emissions to protect them from further harm. When private negotiations between the smelter and the homesteaders stalled, attention shifted toward international diplomacy. Canada and the United States eventually concluded a bilateral treaty, which provided for the smelter to compensate private claimants for harm incurred before 1932 while referring questions about subsequent injuries to arbitration.

The arbitral tribunal delivered its final decision in 1941. Citing national court decisions that held sovereigns responsible for private transboundary pollution, the tribunal reasoned that “under the principles of international law … no State has the right to use or permit the use of its territory in such a manner as to cause injury by fumes in or to the territory of another or the properties or persons therein, when the case is of serious consequence and the injury is established by clear and convincing evidence.”Footnote ¹² This affirmation of the prohibition against transboundary pollution has become a canonical cornerstone of international environmental law.Footnote ¹³

Trail Smelter envisions an international legal order in which states must interact as good neighbors, consistent with principles of equity and sovereign equality.Footnote ¹⁴ As Günther Handl has explained,

Being a good neighbor, in this sense, means states must live with some inconveniences that are inevitable features of communal life. It would be unreasonable, for example, to expect states to exercise such complete control over their territory as to eliminate all risk of transboundary harm. But being a good neighbor also means that states may not simply play territorial sovereignty as a trump card to avoid taking responsibility for serious transboundary harm. They must exercise due diligence, using the resources at their disposal – including legal regulation – to ensure that dangerous activities do not inflict significant injury abroad. When transboundary harm does occur, they must take steps to curtail further injury and provide compensation.Footnote ¹⁶ These obligations are necessary to respect the principle of sovereign equality under international law.

Elementary Considerations of Humanity

Canada and the United States used the Trail Smelter arbitration to bolster their shared commitment to good neighborly relations. However, the legal principles articulated in Trail Smelter would soon receive broader application when the ICJ extended these principles to a dispute between embittered geopolitical adversaries on the other side of the Atlantic.Footnote ¹⁷

On October 22, 1946, two British destroyers struck submerged mines in the Corfu Channel off the coast of Albania. The ensuing blast caused major damage to the destroyers and claimed the lives of over three dozen crew members. The incident marked the culmination of a series of tense standoffs between Albania and the United Kingdom, which had squared off on opposite sides of the nascent Cold War. Earlier the same year, an Albanian battery had fired in the direction of two British cruisers passing through the channel without connecting. The British made a formal diplomatic protest and, in further defiance, sent four warships steaming through the channel. When two of these ships – the Saumarez and the Volage – struck mines, suffering casualties and major damage, the United Kingdom initiated proceedings against Albania in the ICJ.Footnote ¹⁸

A central question in the Corfu Channel Case was whether Albania could be held responsible for the mine blasts. The United Kingdom did not offer any direct evidence to establish that Albania had planted the mines in the channel.Footnote ¹⁹ Nonetheless, the Court concluded that Albania must pay compensation for the United Kingdom’s injuries due to a combination of factors. First, by all accounts, the minefield had been laid in Albanian territorial waters not long before the deadly explosions. Second, during the relevant period, Albania exercised exclusive jurisdiction and continuous oversight over the waters, such that the mines could not have been placed without its knowledge.Footnote ²⁰ Third, Albania did not warn the United Kingdom about the minefield.Footnote ²¹ Under these circumstances, the Court concluded, Albania had a duty to warn the United Kingdom of the impending danger. Albania’s duty to provide notice rested “on certain general and well-recognized principles, namely: elementary considerations of humanity, even more exacting in peace than in war; the principle of the freedom of maritime communication; and every State’s obligation not to allow knowingly its territory to be used for acts contrary to the right of other States.”Footnote ²² Having failed to notify the United Kingdom that its navy risked serious harm by traversing the Corfu Channel, Albania assumed legal responsibility for injuries suffered by the Saumarez, the Volage, and their crews.

By holding that Albania was obligated to provide notice of threats emanating from its territory, the ICJ took a substantial step toward mandatory cooperation. The Corfu Channel judgment gave states like Albania a choice: either eliminate serious dangers themselves (e.g., by removing submerged mines) or cooperate with other states (e.g., by consenting to foreign minesweeping). In either scenario, states could not act without regard to foreign interests. They must take actions reasonably calculated to prevent serious harm to other states, including by affirmatively warning other states of dangers. As the ICJ recognized in Corfu Channel, these minimal requirements to suppress serious threats and provide notice to other states are necessary to respect “elementary considerations of humanity” and honor other states’ equal rights.

Cooperating for Environmental Conservation

States cannot satisfy their due diligence obligations in many contexts without robust cooperation. Consider again the Trail Smelter dispute. In theory, Canada could have shut down the Trail smelter, but this would have delivered a crushing blow to the British Columbian mining industry. Economic and political considerations dictated that Canadian regulators should pursue an intermediate solution, setting emissions standards at levels that would maximize the smelter’s capacity for zinc and lead production without inflicting serious harm across the border in violation of international law. But how much would the smelter have to reduce its emissions to achieve this objective? To answer this question, Canadian regulators would have to conduct a rigorous environmental impact assessment, taking into account wind patterns, terrain, flora, fauna, human settlement, and other factors on the American side of the border. Collecting this information would require the United States’ cooperation. Canada could not realistically satisfy its obligation to regulate harmful transboundary pollution from the smelter without consulting and exchanging information with the United States.

Due diligence also constrained how Canada could handle US objections to its governance of the Trail smelter. As noted above, Canada accepted responsibility for the smelter’s adverse environmental impacts in the 1920s and early 1930s. Nonetheless, Canada continued to resist the United States’ requests to make even more aggressive cuts to the smelter’s pollution. The dispute between the two states centered partly on scientific uncertainty about the smelter’s environmental impact under various atmospheric conditions. However, Canada and the United States also disagreed about what level of harm would be serious enough to trigger the duty to prevent significant harm. Given the indeterminacy of “significant harm” and the triggering conditions of the duty, due diligence required Canada to strive in good faith to pursue further consultation, negotiation, or third-party dispute resolution, such as an independent fact-finding commission, mediation, arbitration, or adjudication. By cooperating with the United States to resolve their factual and legal disagreements in the Court of Arbitration, Canada satisfied the due diligence standard.

The Trail smelter controversy thus illustrates how, in practice, the duty to prevent transboundary harm may generate cooperation that satisfies the due diligence requirements of the prevailing regime of mandatory cooperation. To satisfy the due diligence standard, states must make a reasonable, good-faith effort to investigate risks of significant transboundary harm. They must notify, exchange information, and consult, negotiate, and accept third-party dispute resolution with other states. Only by taking these kinds of steps can they demonstrate due regard for other states’ equal sovereignty and avoid an impermissible abuse of right.

Codifying Mandatory Cooperation

Within the past half-century, mandatory cooperation has become deeply embedded in international environmental law. In June 2022, the international community celebrated the fiftieth anniversary of the first global summit on environmental conservation: the UN Conference on the Human Environment, held in Stockholm, Sweden, June 5–16, 1972. A crowning achievement of the Stockholm Conference was its landmark declaration enshrining “common principles to inspire and guide the peoples of the world in the preservation and enhancement of the human environment.”Footnote ²³ The Stockholm Declaration recognizes the need for “extensive cooperation among nations and action by international organizations in the common interest.”Footnote ²⁴ Although the Stockholm Declaration does not spell out precisely which forms of international cooperation are essential, it does affirm that states have a “responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction.”Footnote ²⁵

After the Stockholm Conference, the international community elaborated duties of cooperation for environmental conservation in a series of treaties, declarations, and other instruments. That same year, the UN General Assembly recognized that international cooperation for the environment, as contemplated in the Stockholm Declaration, demanded that states exchange technical data related to transboundary pollution “in the best spirit of co-operation and good-neighborliness.”Footnote ²⁶ In 1979, the UN Economic Commission for Europe’s (UNECE) Long Range Transboundary Air Pollution Agreement (LRTAP) committed member-states to combat air pollution by exchanging information, consulting, and pursuing collaborative research to identify and eliminate significant threats.Footnote ²⁷ Under LRTAP’s cooperative framework, member states have subsequently established additional protocols to combat some of the most deadly atmospheric pollutants, including sulfur, nitrogen, and volatile organic compounds.Footnote ²⁸ UNECE’s 1992 Convention on Transboundary Effects of Industrial Accidents also obligates states to identify risks of transboundary harm from industrial accidents, share relevant information, and consult with one another to develop effective prevention and mitigation strategies.Footnote ²⁹ When accidents occur, states-parties must notify other interested states, assess transboundary harm, and solicit assistance to address the harm.Footnote ³⁰

Mandatory cooperation also features prominently in treaties addressing oceanic pollution, including the 1982 UN Convention on the Law of the Sea (UNCLOS).Footnote ³¹ In addition to requiring states-parties to prohibit and penalize pollution of the marine environment, UNCLOS demands that they cooperate to prevent significant oceanic pollution and eliminate or reduce its adverse effects on the marine environment.Footnote ³² When states-parties become aware of imminent dangers to the marine environment, they must immediately notify other states that are likely to be impacted.Footnote ³³ In addition, states-parties are obligated to cooperate in “promoting studies, undertaking programmes of scientific research and encouraging the exchange of information and data acquired about pollution of the marine environment” to assess better “the nature and extent of pollution, exposure to it, and its pathways, risks and remedies.”Footnote ³⁴ They must conduct environmental impact assessments for pollution of the marine environment,Footnote ³⁵ and they must cooperate to formulate and elaborate international rules, standards, and best practices for protecting the marine environment.Footnote ³⁶ Similar cooperative obligations appear in other treaties that address marine pollution.Footnote ³⁷ Based on these developments in treaty law and consistent state practice, the International Tribunal for the Law of the Sea (ITLOS) has characterized mandatory cooperation as “a fundamental principle in the prevention of pollution of the marine environment under … general international law.”Footnote ³⁸

Another important codification of mandatory cooperation is the Convention on Environmental Impact Assessment in a Transboundary Context, the product of a UN-sponsored conference in Espoo, Finland (Espoo Convention).Footnote ³⁹ The Espoo Convention requires states-parties to provide notice of activities that are likely to cause a significant adverse transboundary impact.Footnote ⁴⁰ They must also conduct environmental impact assessments for such activities, consult with other interested states regarding preventing or mitigating transboundary harms, and provide mutual assistance in eliminating or reducing such harms.Footnote ⁴¹ When states-parties decide whether to proceed with an activity that may have transboundary impacts, they must take “due account” of the likely effect on other states.Footnote ⁴² Final decisions must be communicated to other states in writing, explaining the reasons and considerations on which decisions are based.Footnote ⁴³ If other states object, states-parties must pursue further consultations to consider alternative courses of action.Footnote ⁴⁴ The Espoo Convention thus offers a detailed roadmap for international cooperation concerning transboundary pollution.Footnote ⁴⁵

In 2008, the UN International Law Commission (ILC) incorporated central features of this burgeoning treaty practice into its Draft Articles on the Prevention of Transboundary Harm from Hazardous Activities (Draft Articles).Footnote ⁴⁶ Consistent with Trail Smelter and Corfu Channel, the Draft Articles provide that states must “take all appropriate measures to prevent significant transboundary harm or at any event to minimize the risk thereof,” and they characterize this obligation as “one of due diligence.”Footnote ⁴⁷ In addition, the Draft Articles demand that states cooperate by providing notice of possible transboundary harm, transmitting relevant technical information about risks, and consulting with one another to “seek solutions based on an equitable balance of interests.”Footnote ⁴⁸ If consultations do not lead to an agreed solution, the state of origin may decide how to proceed, but it must account for the interests of other states.Footnote ⁴⁹ As the ILC has recognized, this approach to transboundary harm draws inspiration from the Lake Lanoux Case discussed in Chapter 2. Like Lake Lanoux, the Draft Articles respect territorial jurisdiction by denying potentially affected states veto power over activities outside their territory. But the Draft Articles also guard against the abuse of territorial sovereignty by requiring states to exercise due diligence to stop activities within their jurisdiction from generating significant transboundary harm.Footnote ⁵⁰ When disputes arise concerning these requirements, the Draft Articles contemplate that states may convene an impartial fact-finding commission or they may settle their disputes through other “peaceful means … chosen by mutual agreement,” such as negotiation, mediation, conciliation, arbitration, or adjudication.Footnote ⁵¹

Cooperating through Courts and Tribunals

In recent years, international courts and tribunals have applied mandatory cooperation to transboundary pollution in a variety of settings. The most important and influential case is the ICJ’s 2010 judgment in a dispute concerning Uruguay’s construction of pulp mills on the River Uruguay.Footnote ⁵² Decades earlier, Argentina and Uruguay had concluded a bilateral treaty establishing detailed rules to govern the river’s use and environmental conservation, and they had established the Administrative Commission of the River Uruguay (CARU) to facilitate conciliation and judicial settlement of disputes.Footnote ⁵³ They also agreed to prepare environmental impact assessments for projects that might impact the river’s water and work through CARU to notify the other party, exchange relevant information, and consult and negotiate over any unresolved concerns.Footnote ⁵⁴ Uruguay took significant steps to comply with these requirements before proceeding with plans to build two pulp mills: it prepared preliminary environmental impact assessments, delivered these assessments to CARU for review, and engaged in consultations with Argentina. Uruguay began constructing the mills, however, before Argentina had a reasonable opportunity to study the possible environmental impacts and before differences between the two states had been resolved.

Fearing significant pollution to the Uruguay River, Argentina initiated proceedings in the ICJ. Argentina asked the ICJ for a judgment that Uruguay had violated the 1975 Statute by proceeding with construction of the two pulp mills without sufficient bilateral cooperation to ensure the river’s environmental conservation. The Court agreed

Citing Corfu Channel, the Court linked these procedural duties to “the principle of prevention,” which, “as a customary rule, has its origins in the due diligence that is required of a State in its territory.”Footnote ⁵⁶ Uruguay’s failure to provide timely notice before authorizing construction was significant, in the Court’s opinion, because “the obligation to notify is intended to create the conditions for successful co-operation between the parties, enabling them to assess the plan’s impact on the river on the basis of the fullest possible information and, if necessary, to negotiate the adjustments needed to avoid the potential damage that it might cause.”Footnote ⁵⁷ Until this consultation and negotiation had concluded, Uruguay was obligated to withhold its authorization for construction; otherwise, “the negotiations between the parties would no longer have any purpose.”Footnote ⁵⁸ Ultimately, however, because Argentina had not presented any conclusive evidence showing that Uruguay’s pulp mills threatened substantial harm to Argentina, the Court declined Argentina’s request to grant compensatory damages and order the closing of the pulp mills.Footnote ⁵⁹ Instead, the Court concluded its judgment by simply affirming that Uruguay had violated its obligations of mandatory cooperation and reminding the parties of their continuing “duty to co-operate with each other” to prevent future pollution.Footnote ⁶⁰ Thus, Pulp Mills cleared the way for Uruguay to continue constructing and operating the disputed pulp mills while encouraging continued cooperation with Argentina through CARU.Footnote ⁶¹

Although Pulp Mills involved legal duties enshrined in a bilateral treaty, international courts and tribunals have recognized that the obligation to cooperate in addressing transboundary pollution applies to the entire international community as a general requirement of customary international law. For example, in the Case Concerning Land Reclamation by Singapore in and Around the Straits of Johor (Land Reclamation),Footnote ⁶² an ITLOS tribunal characterized the duty to cooperate in preventing transboundary environmental harm as a “fundamental principle” not only under UNCLOS but also under “general international law.”Footnote ⁶³ At issue in the case was Malaysia’s challenge to Singapore’s efforts to expand its territory by reclaiming land from the Straits of Johor.Footnote ⁶⁴ Malaysia argued that the project would degrade the marine environment in the straits by adversely impacting the usual patterns of coastal erosion, sedimentation, and water flow through the straits. Malaysia also challenged Singapore’s failure to provide notice, exchange information, and consult and negotiate with Malaysian authorities as required under UNCLOS. While the proceedings were pending, the parties managed to resolve their differences by agreeing to jointly sponsor an environmental impact assessment by an independent body.Footnote ⁶⁵ Singapore also agreed to share relevant information, consult with Malaysian authorities, consider their views, and negotiate toward a mutually acceptable resolution.Footnote ⁶⁶ Accordingly, by the time the tribunal was ready to rule on Malaysia’s claims, the parties had already reached a mutually acceptable path forward consistent with their duties of mandatory cooperation under customary international law. All that remained was for the ITLOS tribunal to incorporate the parties’ agreement into its October 2003 order granting provisional measures.Footnote ⁶⁷

In other proceedings, the ICJ has agreed that under customary international law, the requirements of mandatory cooperation apply to all states in disputes concerning significant transboundary harm. In Certain Activities Carried Out by Nicaragua in the Border Area (San Juan River), Costa Rica and Nicaragua each claimed that the other had violated international law by failing to conduct an environmental impact assessment for works undertaken along the San Juan River.Footnote ⁶⁸ Costa Rica faulted Nicaragua for not undertaking a sufficiently robust environmental impact assessment before commencing a dredging project in the San Juan that might cause harm to the Colorado River and vulnerable wetlands within Costa Rica’s borders.Footnote ⁶⁹ Nicaragua counterclaimed that Costa Rica had failed to conduct an environmental impact assessment for a road it had constructed alongside the river.Footnote ⁷⁰ Quoting Pulp Mills, the Court agreed with the parties that the obligation to undertake an environmental impact assessment for activities that risk transboundary harm “may now be considered a requirement under general international law” that applies even without a binding treaty.Footnote ⁷¹ Nicaragua satisfied this obligation by undertaking a preliminary assessment before beginning its dredging project, the Court concluded,Footnote ⁷² but Costa Rica violated international law by failing to undertake an environmental impact assessment before building the road.Footnote ⁷³

In sum, Pulp Mills, Land Reclamation, and San Juan River illustrate how mandatory cooperation can facilitate peaceful dispute resolution in accordance with equitable principles. When states conduct environmental impact assessments, notify one another of ecological risks, and share other relevant information, they can better understand the harmful impacts of transboundary pollution and develop more effective prevention and mitigation strategies. Through negotiation and third-party dispute resolution, they can reach solutions that equitably accommodate their respective rights and interests.

Catalyzing Environmental Cooperation

At the opening session of the 1972 Stockholm Conference, Secretary-General Maurice Strong declared that the Conference’s aim was “to reconcile man’s legitimate, immediate ambitions with the rights of others, with respect for all life supporting systems, and with the rights of generations yet unborn.”Footnote ⁷⁴ Strong explained that the Stockholm Declaration “holds that all nations must accept responsibility for the consequences of their own actions on environments outside their borders,” and he asserted that “it is essential that this fundamental principle be accepted here if we are to establish a minimum basis for effective international cooperation following this conference.”Footnote ⁷⁵ As Strong correctly perceived, and as this chapter has shown, there is a vital link between state responsibility to prevent transboundary pollution, on the one hand, and international cooperation for environmental protection, on the other. States cannot satisfy their due diligence obligations with respect to transboundary pollution unless they also embrace international cooperation. Put another way, cooperation is necessary for international law to govern transboundary pollution. Once states recognized in Stockholm that they must prevent transboundary pollution, it followed that they would also have to share information, consult, negotiate, and accept third-party dispute resolution to ensure their efforts were effective. Cooperation thus became mandatory under international environmental law.Footnote ⁷⁶

These developments have transformed global governance. As this chapter has shown, states have enshrined the requirements of mandatory cooperation in international environmental treaties; the ILC has endorsed mandatory cooperation in its Draft Articles on Transboundary Harm; and international courts and tribunals have applied the requirements of mandatory cooperation as customary international law. There is no longer any serious doubt that international law obligates states to cooperate with one another to ensure that activities within their jurisdiction do not introduce harmful pollution abroad. But the ramifications of mandatory cooperation for environmental protection run deeper still. Mandatory cooperation has accelerated the progressive development of international environmental law by pressing states to share information, consult, and negotiate with one another. Since Stockholm, states have concluded a host of agreements to combat transboundary pollution, including air pollution,Footnote ⁷⁷ water pollution,Footnote ⁷⁸ hazardous wastes,Footnote ⁷⁹ and nuclear safety.Footnote ⁸⁰ The rapid proliferation of environmental treaties and institutions following the Stockholm Conference reflects the new reality that states are expected to work together as committed partners to address transboundary pollution. Mandatory cooperation has become both a cornerstone of international environmental law and a powerful catalyst for the law’s progressive development.

Much of the development of international environmental law consists of “soft law” instruments rather than legally binding treaties.Footnote ⁸¹ Nonbinding declarations, such as the Stockholm Declaration, the 1992 Rio Declaration on Environment and Development,Footnote ⁸² and the 2002 Johannesburg Declaration on Sustainable Development,Footnote ⁸³ articulate broad principles and suggest best practices for responsible environmental stewardship. Critics sometimes dismiss such nonbinding declarations as phantom laws that compromise international law’s integrity as a normative system.Footnote ⁸⁴ However, reliance on soft commitments need not be viewed as a “pathological phenomenon” that enfeebles international legal order.Footnote ⁸⁵ In the environmental arena, soft law instruments usually reflect serious efforts to bolster states’ political commitments and practical capacities to prevent transboundary environmental harm. When these efforts are successful, they can reduce the need for binding treaties. To the extent states relate to each other as neighbors, they may find ways to resolve their differences through friendly cooperation based on informal norms and practices rather than resort to legal obligations and enforcement.Footnote ⁸⁶ Even if treaties might be preferable in a perfect world, soft law commitments are sometimes the most robust form of normative consensus that states can achieve through diligent cooperation. Mandatory cooperation thus helps to explain and contextualize soft law’s prevalence in international environmental governance, showing why it may be worth celebrating, or at least having, even as the international community continues to pursue more intensive commitments to prevent or minimize transboundary pollution.

Yet despite evident progress, the dangers of transboundary pollution have never been greater. In the next chapter, we consider how mandatory cooperation applies to the supreme existential danger of our time: atmospheric pollution and its devastating contribution to global warming. As we will see, in principle, states must exercise due diligence to prevent carbon emissions from exacerbating global warming. This obligation flows, in part, from the general duty to prevent transboundary harm. Additionally, states now accept that climate change and its adverse effects qualify as a common concern of humanity that is entrusted to the joint stewardship of the international community as a whole. Accordingly, joining the fight against climate change is no longer an option states can take up or refuse; it is mandatory under international law.