2.1. The common interest in compliance with relevant obligations

Even before it introduced the language of obligations erga omnes and erga omnes partes, the ICJ recognised that the international community as a whole, or a group of States, could share a common legal interest in compliance with certain obligations.Footnote ³⁴ While omitting the terminology of obligations erga omnes and erga omnes partes, the Court in the South West Africa cases recognised that the legal interest shared by a group of States may underlie certain obligations so as to entitle each State to seek their enforcement through adjudication. Affirming its jurisdiction in the cases brought by Ethiopia and Liberia, the Court recognised that the then Member States of the League of Nations enjoyed ‘a legal right or interest in the observance by the Mandatory of its obligations both toward the inhabitants of the Mandated Territory, and toward the League of Nations and its Members’.Footnote ³⁵ For Judge Jessup, such legal interests existed in particular in respect of ‘general humanitarian causes’.Footnote ³⁶ Even judges who subsequently supported the dismissal of the cases owing to the lack of a legal interest on the part of the applicant States affirmed the existence, in general terms, of obligations of this character. Judges Spender and Fitzmaurice agreed that States Parties to a treaty may ‘have a legal interest in its due observance, even though the alleged breach of it has not, or not yet, affected them directly’.Footnote ³⁷ Like Judge Jessup, Judge Bustamante took note of the ‘human rights objectives’ of the mandate,Footnote ³⁸ which in his view implied that:

While ultimately dismissing the cases, the Court did not exclude in principle that the Member States of the League of Nations could have shared a legal interest in South Africa’s fulfilment of its obligations. It was the view of the Court, however, that ‘such rights or interests, in order to exist, must be clearly vested in those who claim them … and that in the present case, none were ever vested in individual members of the League’.Footnote ⁴⁰ In contrast, several dissenting judges emphasised the existence of ‘general interests’ under international law as it stood at the timeFootnote ⁴¹ and under the mandate specifically.Footnote ⁴²

Shortly afterwards, the Court in its Barcelona Traction dictum introduced the terminology of ‘obligations erga omnes’, describing these as ‘obligations of a State towards the international community as a whole’ and as obligations which are ‘[b]y their very nature … the concern of all States’.Footnote ⁴³ This language was subsequently recalled in The Wall,Footnote ⁴⁴ Chagos Archipelago Footnote ⁴⁵ and Palestine advisory opinions.Footnote ⁴⁶ The ICJ also relied on the Barcelona Traction dictum to affirm the existence of a common interest in compliance with certain multilateral treaty obligations, which it described as ‘obligations erga omnes partes’, in the cases in which it endorsed the standing of States Parties other than injured States Parties to institute contentious proceedings pertaining to alleged breaches of such obligations. In doing so, the Court retreated from its earlier view in South West Africa that any entitlement to standing based on a common interest in compliance with relevant multilateral treaty obligations must be made explicit.Footnote ⁴⁷

In the Belgium v Senegal case, the Court used the object and purpose of the United Nations (UN) Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment (Torture Convention), articulated in the treaty’s preamble, to demonstrate that States Parties ‘have a common interest to ensure, in view of their shared values, that acts of torture are prevented and that if they occur, their authors do not enjoy impunity’.Footnote ⁴⁸ Where an alleged offender is present in the territory of a given State, this includes a common interest in compliance by that State with the obligations to conduct a preliminary inquiry into the facts and to prosecute the case.Footnote ⁴⁹ Accordingly, the Court concluded that these and any other obligations erga omnes partes contained in the Torture Convention are owed ‘by any State party to all the other States parties’ and ‘each State party has an interest in compliance with them in any given case’.Footnote ⁵⁰ This reasoning supported the Court’s affirmation of Belgium’s standing to bring the case.Footnote ⁵¹ In contrast, for the dissenting Judge Xue, the States Parties ‘in no way intended to create obligations erga omnes partes’ under relevant treaty provisions.Footnote ⁵² Nor was Judge ad hoc Sur convinced by the characterisation of relevant obligations as obligations erga omnes partes, which he did not consider had been ‘justif[ied] in any way’.Footnote ⁵³ The majority failed, in his view, to draw the necessary distinction between those treaty obligations ‘which have an erga omnes character and those which do not’.Footnote ⁵⁴ He opined that multilateral treaties, such as the Torture Convention, cannot, ‘by their nature’ alone, create obligations erga omnes partes.Footnote ⁵⁵ Regrettably, for Judge ad hoc Sur, ‘the object and purpose of the Convention, as determined by the Court, … superseded and removed all other considerations’,Footnote ⁵⁶ including scrutiny of the obligations in question.Footnote ⁵⁷

The ICJ used the same approach to affirm The Gambia’s standing in The Gambia v Myanmar, pointing to the common interest of States Parties to the UN Convention on the Prevention and Punishment of the Crime of Genocide (Genocide Convention)—well established since its Reservations advisory opinionFootnote ⁵⁸ —‘to ensure the prevention, suppression and punishment of genocide’.Footnote ⁵⁹ The Court echoed the language used in Belgium v Senegal to conclude that the ‘common interest in compliance implie[d] that the obligations in question are owed by any State party to all the other States parties’; ‘they are obligations erga omnes partes, in the sense that each State party has an interest in compliance with them in any given case’.Footnote ⁶⁰ The reference to ‘the obligations in question’ was presumably to at least some, if not all, of the obligations alleged by The Gambia to have been breached by Myanmar.Footnote ⁶¹ Judge ad hoc Kreß sought to clarify that, in his view, the common interest of States Parties in compliance did not necessarily mean that ‘each and every obligation contained therein necessarily constitutes an obligation erga omnes partes’.Footnote ⁶² He drew what he considered to be the relevant distinction between obligations ‘central to the fulfilment of the common interest underlying the Genocide Convention’, which he would characterise as obligations erga omnes partes, and those ‘markedly peripheral’ to such an objective.Footnote ⁶³ It was not necessary, in the opinion of the Judge ad hoc, for the Court to have ‘elaborate[d] in more detail on what it takes for an obligation, enshrined in a convention, to “transcend the sphere of bilateral relations of the States parties” so as to acquire an erga omnes partes character’.Footnote ⁶⁴ As in Belgium v Senegal, Judge Xue objected that ‘the notions of obligations erga omnes or erga omnes partes were not established in general international law’ at the time of the drafting of the Genocide Convention and that their enforcement by States Parties other than an injured State Party could not have been intended by the drafters.Footnote ⁶⁵ She was also concerned, more generally, that ‘such common interest’, and thus obligations erga omnes partes, ‘could equally be identified in many other conventions relating, for example, to human rights, disarmament and [the] environment’.Footnote ⁶⁶

The common interest in compliance with the obligations erga omnes partes contained in the Torture Convention and Genocide Convention, respectively, was affirmed in the ICJ’s orders indicating provisional measures in Canada and the Netherlands v Syria Footnote ⁶⁷ and South Africa v Israel.Footnote ⁶⁸ As before, in neither instance did the Court specify whether such a characterisation applied to all the obligations arising under the relevant treaty and, if not, to which obligations such a characterisation did apply. Judge Xue, consistently with her earlier position, did not consider that the ‘common interest’ of States Parties to the Torture Convention gave the applicant States in Canada and the Netherlands v Syria the entitlement to institute the proceedings.Footnote ⁶⁹ In contrast, in South Africa v Israel, the same judge considered that when it came to ‘a protected group such as the Palestinian people, it is least controversial that the international community has a common interest in its protection’.Footnote ⁷⁰ In her view, ‘this is the very type of case where the Court should recognize the legal standing of a State party to the Genocide Convention to institute proceedings on the basis of erga omnes partes’.Footnote ⁷¹

2.2. The importance of the rights underlying relevant obligations

In the Barcelona Traction case, the ICJ did not stop at describing obligations erga omnes as obligations ‘towards the international community as a whole’, which are ‘the concern of all States’.Footnote ⁷² The Court explained further that it was ‘[i]n view of the importance of the rights involved’ that ‘all States can be held to have a legal interest in their protection’.Footnote ⁷³ It gave as examples obligations ‘deriv[ing] … from the outlawing of acts of aggression, and of genocide, and also from the principles and rules concerning the basic rights of the human person, including protection from slavery and racial discrimination’.Footnote ⁷⁴ While some ‘corresponding rights of protection’ had, in the Court’s view, ‘entered into the body of general international law’, ‘others [we]re conferred by international instruments of a universal or quasi-universal character’.Footnote ⁷⁵ Notably, the Court avoided any reference to peremptory norms of international law, whose inclusion in the Vienna Convention on the Law of Treaties was, at the time, new and somewhat controversial.Footnote ⁷⁶ That the Court characterised obligations erga omnes by reference to the importance of the rights underlying them was also the understanding within the ILC.Footnote ⁷⁷

What may well have been a passing remark the Court saw fit to make in the aftermath of the South West Africa cases has since become an integral part of its articulation of obligations erga omnes and erga omnes partes.Footnote ⁷⁸ The reference to ‘the importance of the rights involved’ to describe obligations erga omnes was recalled over 30 years later in the advisory opinion in The Wall, on which basis the Court concluded that the obligations erga omnes breached by Israel included the obligation ‘to respect the right of the Palestinian people to self-determination’ and ‘certain … obligations under international humanitarian law’.Footnote ⁷⁹ The Court further justified its characterisation of relevant obligations under international humanitarian law as obligations erga omnes on the basis that they are ‘so fundamental to the respect of the human person’ and ‘constitute intransgressible principles of international customary law’, a description it had previously given to such obligations in the Nuclear Weapons advisory opinion,Footnote ⁸⁰ and which it repeated in its recent Palestine advisory opinion.Footnote ⁸¹ Judge Higgins, while sceptical of the majority’s characterisation of these obligations as obligations erga omnes,Footnote ⁸² nevertheless agreed that ‘there are certain rights in which, by reason of their importance, “all states have a legal interest in their protection”’.Footnote ⁸³

Subsequent cases in which the common interest in compliance with obligations erga omnes or erga omnes partes was invoked also referred to the importance of the rights corresponding to relevant obligations to do so, even where the treaties in question did not actually confer any such rights on individuals or groups.Footnote ⁸⁴ The Belgium v Senegal decision described the legal interest of States Parties to the Torture Convention in ‘the protection of the rights involved’, citing the Barcelona Traction dictum on the point.Footnote ⁸⁵ This language was recalled again vis-à-vis the Torture Convention in the order indicating provisional measures in the ongoing case of Canada and the Netherlands v Syria.Footnote ⁸⁶ The Palestine advisory opinion, like The Wall advisory opinion, repeated the Barcelona Traction reference to ‘the importance of the rights involved’Footnote ⁸⁷ and concluded that the obligations erga omnes violated by Israel included:

For the Court, ‘a great many of the rules’ of the Geneva Convention relative to the Protection of Civilian Persons in Times of War in particular are ‘so fundamental to the respect of the human person, and elementary considerations of humanity’, that they ‘constitute intransgressible principles of international customary international law’ and ‘incorporate obligations which are essentially of an erga omnes character’.Footnote ⁸⁹

In some cases, individual judges described obligations erga omnes or obligations erga omnes partes as obligations protecting important values rather than, or alongside, important rights. In her declaration appended to the Chagos Archipelago advisory opinion, Judge Xue emphasised ‘the paramount importance of the principle of self-determination’, which was ‘reflected in its erga omnes character’.Footnote ⁹⁰ For Judge Robinson, writing in the same context, the examples of obligations erga omnes given by the Court in its Barcelona Traction dictum ‘[i]ndicate[d] that the essence of obligations erga omnes is that they protect the fundamental values of the international community, such as those relating to respect for the inherent dignity and worth of the human person, the prohibition of aggression and genocide’.Footnote ⁹¹ Similarly, in The Gambia v Myanmar, Judge ad hoc Kreß considered that the erga omnes partes character of relevant obligations in the Genocide Convention was justified not merely by ‘the shared interest that all States parties have in the preservation of the legal régime established by a multilateral treaty’.Footnote ⁹² It was also relevant that ‘the Genocide Convention serves a much more pronounced common interest in that it recognizes and protects a fundamentally important common value’.Footnote ⁹³

The Barcelona Traction reference to ‘the importance of the rights involved’ is the root of some unfortunate terminological and conceptual confusion in subsequent jurisprudence.Footnote ⁹⁴ The Court has referred, on more than one occasion, to ‘rights erga omnes’ either in the place of, or alongside, ‘obligations erga omnes’.Footnote ⁹⁵ The term ‘rights erga omnes’ was usually taken to refer to the interests of individuals or groups who were the beneficiaries of relevant obligations. In the East Timor case, Portugal argued, inter alia, that the rights allegedly breached by Australia were ‘rights erga omnes’, suggesting that this entitled it to require Australia ‘to respect them’ regardless of whether Indonesia had ‘conducted itself in a similarly unlawful manner’.Footnote ⁹⁶ The Court used the same language when it confirmed that the right of peoples to self-determination, rather than any obligation arising out of it, ‘has an erga omnes character’.Footnote ⁹⁷ Compounding the confusion, the Court referred, in the same figurative breath, to the irrelevance of ‘the nature of the obligations invoked’ when it affirmed the applicability to the case of the ‘indispensable third party’ rule.Footnote ⁹⁸ The language of ‘rights erga omnes’ was recalled again in The Wall advisory opinion,Footnote ⁹⁹ with the majority referring further, and in looser terms still, to ‘the character and the importance of the rights and obligations involved’.Footnote ¹⁰⁰ The Court subsequently reverted to the language of ‘obligations erga omnes’ to describe the obligation to respect the right of peoples to self-determination in the Chagos Archipelago advisory opinion.Footnote ¹⁰¹ Only one judge in that case referred, as the Court had previously done, to the ‘erga omnes character’ of the ‘right of peoples to self-determination’.Footnote ¹⁰² Like the Chagos Archipelago advisory opinion, the more recent Palestine advisory opinion preferred the language of ‘obligations erga omnes’ to that of ‘rights erga omnes’.Footnote ¹⁰³ As before, this did not dissuade individual judges from referring to ‘rights and obligations erga omnes’Footnote ¹⁰⁴ and from characterising the right to self-determination as a ‘right erga omnes’.Footnote ¹⁰⁵

Beyond the various inconsistent references to ‘obligations’ and ‘rights’ erga omnes, the importance of the rights underlying obligations owed erga omnes and erga omnes partes was also used by the ICJ to suggest that the breach of obligations erga omnes and erga omnes partes triggers obligations for States other than injured States. In The Wall advisory opinion, the Court, following its characterisation of relevant obligations as obligations erga omnes, referred to ‘the character and the importance of the rights and obligations involved’ to conclude that all States were under an obligation ‘not to recognize the illegal situation resulting from the construction of the wall’, ‘not to render aid or assistance in maintaining the situation’ and ‘to see to it that any impediment, resulting from the construction of the wall, to the exercise by the Palestinian people of its right to self-determination is brought to an end’.Footnote ¹⁰⁶ In the Chagos Archipelago advisory opinion, the Court concluded, on the back of its characterisation of the obligation to respect the right to self-determination as an obligation erga omnes, that ‘all Member States must co-operate with the United Nations’ to give effect to ‘the modalities required to ensure the completion of the decolonization of Mauritius’.Footnote ¹⁰⁷ The same approach was taken in the Palestine advisory opinion, wherein the Court concluded, again ‘in view of the character and importance of the rights and obligations involved’, that all States are obliged ‘not to recognize as legal the situation arising from the unlawful presence of Israel in the Occupied Palestinian Territory’, ‘not to render aid or assistance in maintaining the situation’ and ‘to ensure that any impediment resulting from the illegal presence of Israel in the Occupied Palestinian Territory to the exercise of the Palestinian people of its right to self-determination is brought to an end’.Footnote ¹⁰⁸ Going beyond its previous jurisprudence, the Court also declared that, ‘in view of the serious breaches of obligations erga omnes’, ‘[t]he duty of non-recognition … applies to international organizations, including the United Nations’.Footnote ¹⁰⁹ In yet another departure from its case law, elsewhere the Palestine advisory opinion declared that ‘in cases of foreign occupation … the right to self-determination constitutes a peremptory norm of international law’.Footnote ¹¹⁰ Given the Court’s references to both obligations erga omnes and peremptory norms, Judge Cleveland sought to make clear that it was the erga omnes nature of the obligations breached, rather than any peremptory status, that gave rise to obligations on the part of other States and the UN.Footnote ¹¹¹ In her view, this is both ‘consistent with the Court’s prior case law’ and the ‘correct’ approach.Footnote ¹¹²

In contrast, other judges writing separately in the advisory opinions took the Court’s various references to ‘the character and the importance of the rights and obligations involved’ as references to their peremptory status.Footnote ¹¹³ Some judges also took issue, in principled terms, with what they saw as the Court’s reliance on the character of the obligations breached as obligations erga omnes or erga omnes partes to support the existence of obligations for other States and, as per the Palestine advisory opinion, international organisations. Judge Higgins, in her separate opinion in The Wall, objected to the majority’s invocation of the Barcelona Traction dictum ‘for more than it can bear’, explaining that the concept of obligations erga omnes discussed therein had ‘nothing to do with imposing substantive obligations on third parties to a case’.Footnote ¹¹⁴ The articulation of obligations erga omnes in the Barcelona Traction case had, in her view, been ‘directed to a very specific issue of jurisdictional locus standi’.Footnote ¹¹⁵ Judge Kooijmans hinted at the same concern.Footnote ¹¹⁶ For Judge Cançado Trindade, writing separately in the Chagos Archipelago advisory opinion, the Court should not have referred ‘only to obligations erga omnes without focusing and elaborating on jus cogens wherefrom they ensue’.Footnote ¹¹⁷ It was necessary, in his view, to ‘elaborate [the Court’s] reasoning on jus cogens (not only obligations erga omnes) and its legal consequences’.Footnote ¹¹⁸ Judges Sebutinde and Robinson, each writing separately to the same opinion, were more explicit in drawing the link between the serious breach of a peremptory norm of international law, rather than the breach of an obligation erga omnes or erga omnes partes, and relevant consequences for other States.Footnote ¹¹⁹

Most recently, in the context of the Palestine advisory opinion, Judge Gómez Robledo, recalling Article 41 ARSIWA, regretted that the Court did not ‘directly establish[] the link between the finding that the right to self-determination has the status of a peremptory norm and the consequences of its violation’.Footnote ¹²⁰ The ‘hierarchically higher’ status of the right to self-determination was not, in his view, founded in the fact that the right gave rise to obligations erga omnes.Footnote ¹²¹ Likewise, Judge Tladi, who had been the ILC’s Special Rapporteur on peremptory norms, lamented that the Court did not ‘pronounce itself clearly on the peremptory status of norms that are widely accepted as having that character’ and instead invoked ‘the related but distinct concept of erga omnes’.Footnote ¹²² The Court’s resort to obligations erga omnes gave Judge Tladi ‘cause for pause’, since ‘this language might suggest that the obligations for third States … flow not from the peremptory status of the right of self-determination but rather from the erga omnes character of the obligations breached’.Footnote ¹²³ For Judge Tladi, the majority’s approach was ‘based on a complete miscomprehension of the relationship between peremptory norms and erga omnes obligations’ and was contrary to the views of States, the ILC and the scholarship.Footnote ¹²⁴ In his view, ‘[t]he erga omnes character of an obligation’, which entitles States other than injured States to invoke responsibility for a breach, is ‘a consequence of the nature of the norm from which the obligation arises’.Footnote ¹²⁵ It ‘does not itself create obligation [sic] on third States’.Footnote ¹²⁶ Were this the case, breaches of obligations erga omnes and erga omnes partes concerning common spaces, in addition to those with ‘primarily humanitarian objectives’, could give rise to ‘the threefold duties of non-recognition, non-assistance and co-operation’ on the part of other States.Footnote ¹²⁷

2.3. The gap in the enforcement by injured States of relevant obligations

The Barcelona Traction dictum relied explicitly on ‘the importance of the rights involved’ to conclude that ‘all States can be held to have a legal interest in the[] protection’ of obligations erga omnes.Footnote ¹²⁸ Yet the same dictum could also be taken to reflect a different characterisation of obligations erga omnes, based on the structure of their performance. This latter characterisation is supported by the Court’s drawing of ‘an essential distinction’ between obligations in the field of diplomatic protection and obligations erga omnes.Footnote ¹²⁹ While obligations relating to diplomatic protection give rise to bilateral obligations between States, obligations erga omnes are non-synallagmatic or ‘non-bilateralisable’.Footnote ¹³⁰ When it comes to the latter, the conduct in performance of the obligation towards one State also fulfils the obligation towards all the others.Footnote ¹³¹ Conversely, the breach of the obligation towards one State necessarily involves the breach of the obligation towards all the others.Footnote ¹³² ILC members like Special Rapporteur Arangio-Ruiz specifically endorsed this articulation of obligations erga omnes rather than the assessment of ‘the importance of the rights involved’:Footnote ¹³³

Like his predecessor, Special Rapporteur Crawford was reluctant to describe obligations erga omnes as ‘necessarily imperative or of fundamental importance to the international community’.Footnote ¹³⁵

Whatever the judges of the ICJ may have intended in drawing a line between obligations in the field of diplomatic protection and obligations erga omnes, and whatever the view preferred within the ILC, many of the obligations recognised by the Court to be obligations erga omnes in the Barcelona Traction dictum, such as the prohibition of aggression,Footnote ¹³⁶ are ‘perfectly bilateralisable’.Footnote ¹³⁷ Nor does the subsequent jurisprudence clearly support an understanding of obligations erga omnes or erga omnes partes based on their non-synallagmatic nature. The Court has done no more than indicate, in relation to obligations erga omnes partes, that relevant obligations are owed ‘by any State party to all the other States parties’.Footnote ¹³⁸ Only Judge Tladi, writing separately in the Palestine advisory opinion, additionally described obligations erga omnes as encompassing both obligations with underlying humanitarian objectives and ‘[o]bligations arising from customary international law norms concerning common spaces’,Footnote ¹³⁹ in the latter case ‘because of their very character as not being capable of being owed bilaterally’.Footnote ¹⁴⁰

Notwithstanding the absence of any formal endorsement by the ICJ of the non-synallagmatic nature of obligations erga omnes and erga omnes partes, or the ‘structural approach’ to articulating such obligations,Footnote ¹⁴¹ the Court has acknowledged more than once that the structure of performance of certain obligations is such that their breach will not necessarily injure another State, precluding, in turn, the enforcement of such obligations by an injured State. Since the South West Africa cases, this fact has been used by the Court to categorise certain obligations as obligations erga omnes partes or to support the standing of States other than injured States to invoke responsibility in the event of the breach of relevant obligations. Setting aside the views expressed by some judges, this approach was not taken by the Court in relation to obligations erga omnes.

When dismissing the South West Africa cases, the Court engaged with, but ultimately rejected, the argument that if the Member States of the League of Nations were not entitled individually to seek the performance of South Africa’s mandate for South West Africa, there would be ‘no entity’ entitled to do so.Footnote ¹⁴² For the majority, it was impermissible to remedy this reality by ‘postulat[ing] the existence of … rights’ in order to avoid a gap in the enforceability of South Africa’s obligations.Footnote ¹⁴³ The Court declined the task of ‘filling in the gaps’ since, in its view, ‘[r]ights cannot be presumed to exist merely because it might seem desirable that they should’.Footnote ¹⁴⁴ Support for the argument was nevertheless seen in the dissenting opinion of Judge Koo, who endorsed the entitlement of Member States of the League of Nations ‘to invoke, in the last resort, judicial protection of the sacred trust’.Footnote ¹⁴⁵ Similarly, Judge Mbafeno regretted that ‘[t]he Court’s interpretation of the Mandate, pursued to its logical conclusion, le[ft] the Mandatory without any enforceable obligations’ in relation to the provisions in question.Footnote ¹⁴⁶

Expressing similar dissatisfaction with gaps in the enforcement of obligations under international humanitarian law and international human rights law, Judge Simma, writing separately in the DRC v Uganda case, considered that Uganda in principle enjoyed standing in respect of its counterclaim alleging violations by the Democratic Republic of the Congo of obligations vis-à-vis non-Ugandan nationals. He described various obligations contained in the International Covenant on Civil and Political Rights, the African Charter on Human and Peoples’ Rights and the Torture ConventionFootnote ¹⁴⁷ as ‘instances par excellence of obligations that are owed to a group of States … and are established for the protection of a collective interest of the States parties’.Footnote ¹⁴⁸ In Judge Simma’s view, ‘at least the core of the obligations deriving from international humanitarian law and human rights law are valid erga omnes’.Footnote ¹⁴⁹ Writing in his academic capacity, he explained that ‘the very raison d’être of at least certain obligations erga omnes’,Footnote ¹⁵⁰ whose breach does not necessarily give rise to injury, implies that States other than injured States must be entitled to invoke the responsibility of the wrongdoing State, ‘so as to make the most important community interests enforceable’.Footnote ¹⁵¹

In the apparent reversal of its position in South West Africa, the Court, on two subsequent occasions, invoked the necessity of ensuring the enforceability of obligations erga omnes partes in multilateral treaties to support its endorsement of the standing of States Parties in the event of a breach and in the absence of injury. In Belgium v Senegal, the Court explained that, were a special interest required for the purpose of ‘mak[ing] a claim concerning the cessation of an alleged breach’ of the obligations erga omnes partes contained in the Torture Convention, ‘in many cases no State would be in the position to make such a claim’.Footnote ¹⁵² Accordingly, ‘any State party to the Convention may invoke the responsibility of another State party with a view to ascertaining the alleged failure to comply with its obligations erga omnes partes … and to bring that failure to an end’.Footnote ¹⁵³ Judge Donoghue, in her declaration, agreed that ‘the obligations at issue could be entirely hollow unless they are obligations erga omnes partes’.Footnote ¹⁵⁴ Conversely, Judge Xue was sceptical of the need to permit States Parties to the Torture Convention other than those with a special interest in compliance to institute contentious proceedings before the Court. In her view, the compliance mechanisms set out in the Torture Convention are meant precisely to address the enforcement of treaty obligations.Footnote ¹⁵⁵ More recently, Judge Xue also expressed concern that such a ‘policing role’ for States Parties to the Torture Convention would be exercised in a ‘selective and biased manner’.Footnote ¹⁵⁶

The same gap-filling logic was used by the majority in The Gambia v Myanmar to reject Myanmar’s argument that only a State Party with a special interest in compliance was entitled to bring a case against it under the Genocide Convention. In language similar to that used in Belgium v Senegal, the Court declared that:

The Court pointed to the fact that ‘victims of genocide are often nationals of the State allegedly in breach of its obligations erga omnes partes’, hinting that, in the event of such a breach, no other State Party would be injured and in a position to institute proceedings.Footnote ¹⁵⁸ At the same time, the Court seemed to indicate that, were another State to have been specially affected by Myanmar’s alleged breach, this would ‘not preclude The Gambia’s standing’.Footnote ¹⁵⁹ Judge ad hoc Kreß, writing separately, considered that ‘it would have been wrong had the Court … left the fundamental community interest at issue … without the judicial protection which is due to it under the applicable law’.Footnote ¹⁶⁰ Considering the insufficiency of the enforcement of certain obligations erga omnes or erga omnes partes by a State with a special interest in compliance, the Judge ad hoc proposed the division of obligations erga omnes and erga omnes partes into two subsets. The first subset encompassed obligations in respect of which ‘the collective interest at stake is mediated through the special legal interest of at least one State’.Footnote ¹⁶¹ That is, for obligations such as the prohibition of the use of force (presumably taken to be an obligation owed erga omnes or erga omnes partes), ‘the collective interest comes into play through the violation of the special legal interest of at least one direct victim State’.Footnote ¹⁶² The second subset included obligations, such as the prohibition of genocide, in respect of which ‘the collective interest … is not mediated through the special legal interest of any State’.Footnote ¹⁶³ In the event of the breach of such an obligation, Judge ad hoc Kreß explained that ‘no State is in a position to dispose of the relevant collective interest completely’.Footnote ¹⁶⁴ He did not specify, however, whether acts of genocide attributable to one State and directed at a group comprising the nationals of another State would, like the prohibition of the use of force, be obligations in respect of which ‘the collective interest comes into play through the violation of the special legal interest of at least one direct victim State’.Footnote ¹⁶⁵ Judge Xue, for her part, considered that the permissibility of reservations to the Genocide Convention, including to exclude the application of the treaty’s compromissory clause,Footnote ¹⁶⁶ ‘could also lead to many situations where no State party would be in a position to make a claim before the Court against another State party who has made a reservation to the jurisdiction of the Court’.Footnote ¹⁶⁷ Such reservations did not, in her view, ‘prejudice[] the common interest of the States parties to the Convention’; they only ‘exclude[d] a particular method of settling a dispute’ arising under the Convention.Footnote ¹⁶⁸

Notably, the gap-filling logic proposed by the Court in Belgium v Senegal and The Gambia v Myanmar was not seen in the Australia v Japan case, brought by Australia with a view to ‘uphold[ing] its collective interest’ in Japan’s compliance with its obligations under the International Convention for the Regulation of Whaling and decided by the Court not long after Belgium v Senegal.Footnote ¹⁶⁹ Barring a clarification sought during oral proceedings, the question of Australia’s standing to bring the case was not raised.

3.1. Implications for the breadth of the classes of obligations erga omnes and erga omnes partes

Besides demonstrating a common interest in compliance with obligations erga omnes and erga omnes partes—an easily satisfied requirement,Footnote ¹⁷⁴ consistently affirmed by the ICJFootnote ¹⁷⁵ —the use of two further grounds for characterising obligations as obligations erga omnes or erga omnes partes, namely the assessment of ‘the importance of the rights involved’Footnote ¹⁷⁶ and the absence of injury in the event of a breach, indicates that, in the view of the Court:

Beyond the assessment of the common interest, which of these two approaches is used to affirm an obligation’s status as erga omnes or erga omnes partes, or their application cumulatively to this end, determines how narrowly or widely the classes of obligations erga omnes and erga omnes partes are construed. Different approaches to obligations erga omnes and obligations erga omnes partes might also be suggested. One commentator, for example, proposes to define obligations erga omnes by reference to the importance of the rights involved and obligations erga omnes partes by their non-synallagmatic nature. On this view, obligations erga omnes ‘exist as such because of the community interest in their fulfilment—by reason of the “importance of the rights involved”’.Footnote ¹⁷⁸ In contrast, obligations erga omnes partes are obligations ‘of such a structure that their breach would not result in an injured State’.Footnote ¹⁷⁹ To be sure, the Barcelona Traction dictum, in its reliance on ‘the importance of the rights involved’, referred only to obligations erga omnes and not obligations erga omnes partes.Footnote ¹⁸⁰ Yet the reference in substance included obligations ‘conferred by international instruments of a universal or quasi-universal character’.Footnote ¹⁸¹ The Court’s description of obligations erga omnes partes in contemporary practice, moreover, suggests the relevance in that context too of ‘the importance of the rights involved’.Footnote ¹⁸² Conversely, the Court’s reliance on the non-synallagmatic nature of certain obligations has to date been limited to its articulation of obligations erga omnes partes,Footnote ¹⁸³ but there is no clear reason to apply the logic only to obligations owed to a group of States and not to all States. As such, the following discussion considers the implications of each approach for the characterisation of both obligations erga omnes and obligations erga omnes partes.

3.2. Implications for the identification of obligations erga omnes partes in multilateral treaties

The various points of jurisprudential inconsistency notwithstanding, the ICJ has been consistent in its articulation of obligations erga omnes and erga omnes partes by reference to the common interest of ‘the international community as a whole’Footnote ²²⁵ or a group of States,Footnote ²²⁶ as the case may be, in compliance with relevant obligations.Footnote ²²⁷ When it comes specifically to the obligations erga omnes partes contained in multilateral treaties, the Court has not, since the South West Africa cases, required the express articulation of such a legal interest. Instead, the common interest of the States Parties in the performance of relevant obligations was inferred by the Court from its assessment of the object and purpose of the treaty at issue.Footnote ²²⁸

The sufficiency of characterising treaty obligations as obligations erga omnes partes by reference to the common interest of States Parties, as reflected in the object and purpose of a treaty, is doubtful.Footnote ²²⁹ First, there is a risk of any and every multilateral treaty being characterised as one established for the protection of the common interest of its States Parties and therefore as a treaty encompassing obligations erga omnes partes. As one commentator rightly asks: ‘[w]hich international obligations are not in some sense “established for the protection of a collective interest”?’Footnote ²³⁰ Moreover, the practice leaves unclear whether, in the case of a multilateral treaty whose object and purpose is said to reflect the common interest of its States Parties, all the obligations contained therein are necessarily obligations erga omnes partes, the breach of which entails all relevant consequences in the law of State responsibility, entitles States Parties to have standing before the Court even in the absence of injury on their part and implies further consequences for the Court’s procedure.Footnote ²³¹ Judges ad hoc Sur and Kreß, writing separately in different cases, were both of the view that not every obligation contained in a multilateral treaty reflecting the common interest of its States Parties is necessarily an obligation erga omnes partes.Footnote ²³² For Judge ad hoc Sur, dissenting in Belgium v Senegal, the ‘nature’ of a multilateral treaty like the Torture Convention is insufficient in itself to justify the characterisation of the obligations contained therein as obligations erga omnes partes.Footnote ²³³ Nor should the consideration of the object and purpose of the treaty supersede other relevant considerations, in particular, the interpretation of the obligations allegedly breached.Footnote ²³⁴ In The Gambia v Myanmar, Judge ad hoc Kreß qualified the majority’s reliance on the object and purpose of the Genocide Convention to characterise relevant obligations as obligations erga omnes partes, suggesting that only obligations ‘central to the fulfilment of the common interest’ underlying the Convention, and not those ‘markedly peripheral’ to such an objective, could be described as such.Footnote ²³⁵ Commentators agree that not every obligation in a multilateral treaty reflecting the common interest of its States Parties is an obligation erga omnes partes.Footnote ²³⁶

The existence of a common interest among the States Parties to a multilateral treaty is indeed of little assistance in assessing whether a particular obligation contained in such a treaty is an obligation erga omnes partes.Footnote ²³⁷ With insufficient guidance from the Court, however, it remains unclear how to undertake such an assessment. One approach is to argue, by analogy, that only obligations qualitatively comparable to those already characterised by the Court as obligations erga omnes partes are obligations erga omnes partes. In Belgium v Senegal, these were the obligation of a State Party to ‘immediately make a preliminary inquiry into the facts’ when ‘a person alleged to have committed’ relevant offences is in its territoryFootnote ²³⁸ and, where the State does not extradite him or her, the obligation to prosecuteFootnote ²³⁹ such a person.Footnote ²⁴⁰ For Judge ad hoc Kreß, if not also the majority in the decision on preliminary objections in The Gambia v Myanmar, ‘the obligations said by The Gambia to have been violated by Myanmar’ under the Genocide Convention are also obligations erga omnes partes.Footnote ²⁴¹ This includes the obligation to prevent and punish the crime of genocide, the prohibition of relevant acts of genocide, the obligation to punish acts of genocide, the obligation to enact relevant legislation under municipal law and the obligation to prosecute persons ‘charged with genocide’ before a competent tribunal.Footnote ²⁴² Some commentators include, by extension, comparable obligations relating to ‘core offenses’ under other multilateral treaties.Footnote ²⁴³

While pragmatic, such an approach risks being overly restrictive in light of the limited case law on the point and, in any event, ‘the demarcation of conventional obligations that are erga omnes from those that are not … requires a principled distinction’.Footnote ²⁴⁴ Reflecting the incoherence in the Court’s articulation of obligations erga omnes and erga omnes partes, scholarly suggestions as to how to assess whether an obligation contained in a multilateral treaty is an obligation erga omnes partes either call for the weighing of the importance of an obligation for the fulfilment of the object and purpose of the treaty or rely on the non-synallagmatic nature of the obligation.Footnote ²⁴⁵ Representing the first approach are those who, like Judge ad hoc Kreß,Footnote ²⁴⁶ ask whether relevant obligations ‘are essential to fulfilling the aim of the treaty’.Footnote ²⁴⁷ These commentators propose an assessment of whether the provision in question is ‘relevant’ to the common interest reflected in the treaty,Footnote ²⁴⁸ variously describing obligations erga omnes partes as ‘obligations that would defeat the “object and purpose” of the treaty’,Footnote ²⁴⁹ obligations which ‘go to the fundamental purpose of the treaty’Footnote ²⁵⁰ and obligations ‘incorporated to achieve th[e] common interest’ underlying the treaty.Footnote ²⁵¹ In line with this approach, commentators conclude, for example, that ‘reporting obligations’ contained in relevant treaties do not qualify as obligations erga omnes partes.Footnote ²⁵² Committed to the second approach are those who, like Judge Tladi,Footnote ²⁵³ consider the non-synallagmatic structure of performance of obligations relevant to their characterisation as obligations erga omnes partes.Footnote ²⁵⁴ Even commentators who, in principle, support the identification of obligations erga omnes partes by reference to their centrality to the object and purpose of the treaty recognise, against the backdrop of the Court’s recent practice, some place for a gap-filling rationale vis-à-vis non-synallagmatic obligations. The admission is made in particular in the context of multilateral human rights treaties, which impose obligations on States Parties in respect of conduct within their own jurisdictions and whose breach is unlikely, in many instances, to cause injury to any other State Party.Footnote ²⁵⁵

Without sufficient clarity from the Court, some commentators employ a combination of rationales to justify the erga omnes partes status of obligations.Footnote ²⁵⁶ Others introduce policy considerations to rule out the characterisation of certain obligations, such as procedural obligations,Footnote ²⁵⁷ as obligations erga omnes partes because doing so would be ‘unimaginable’Footnote ²⁵⁸ or have ‘far-reaching effects’Footnote ²⁵⁹ in terms of the breadth of the entitlement to standing on the part of non-injured States Parties.

In the end, it is insufficient to characterise obligations erga omnes partes by reference to the common interest of States Parties to a multilateral treaty, but how to do so remains unclear. On the one hand, identifying obligations erga omnes partes by assessing the importance of the obligation to the fulfilment of the object and purpose of a multilateral treaty leaves room for judgment, which might be exercised by the Court to circumscribe what would otherwise constitute an unwieldy set of obligations erga omnes partes contained in relevant treaties. On the other hand, it cannot be denied that the performance of certain multilateral treaty obligations is owed collectively by each State Party to all the others, rather than to each of them bilaterally. The need to ensure the enforceability of such obligations supports their characterisation as obligations erga omnes partes. It remains for the Court to determine the implications of this reality, both in the context of multilateral treaties and for the characterisation of obligations erga omnes.