At war? Party status and the war in Ukraine

Abstract Military support to Ukraine has been accompanied by debates as to when Western states would find themselves ‘at war’ with Russia. This political and legal discourse reminds us that international law needs concepts to identify who is a party to an international armed conflict. Identifying parties is crucial because the international legal regulation of armed conflict remains, in many ways, structured by reference to party status – even if the legal meaning of being a party today differs significantly from the traditional implications of being ‘at war’. To capture the increasingly complex co-operation patterns of today’s and tomorrow’s wars, this article identifies the contours for a framework of legal criteria for establishing when a state has become a party to an ongoing international armed conflict. To become a party under this framework, a state must knowingly make a contribution to the conflict that is of a character such that it is directly connected to harm caused to the adversary. That contribution must be sufficiently closely co-ordinated with fellow parties to allow for involvement in the decision-making processes regarding co-ordinated military operations. Applying these criteria to key support scenarios, as exemplified in Russia’s war against Ukraine, permits reasonable distinctions, also with a view to future conflicts. More widely, the analysis of party status may enhance our understanding of the architecture of the international legal regulation of armed conflict as a whole, and its ability to respond to the realities of contemporary conflicts.


Introduction
In Ukraine's existential struggle against Russia's aggression, many states have delivered weapons and other military equipment to Ukraine and trained Ukrainian soldiers to use those materials. 1 Moreover, some statesmost notably the UShave shared battlefield intelligence with Ukraine 2 and disrupted Russian cyber operations and communication channels. 3 As military assistance to Ukraine has scaled up, 4 one question has taken centre stage: When would Western states, themselves, be 'at war' with Russia? 5 Western states have emphasized that they would not take steps that would render them parties to the conflict under international law. 6 Conversely, Russia has warned that it would consider certain Western assistance as participation in the conflict. 7 This public discourse on the war in Ukraine reveals a need for reflection on how we establish who is 'at war'. It is a challenging and crucial question because states have always worked together to wage wars. 8 Facilitated by technological advancements, co-operation is one of the most salient features of contemporary armed conflicts. 9 The war in Ukraine has been described as 'the final war of 20 th -century militaries' because of certain means and methods of warfare that have been employed. 10 By contrast, the diverse forms of inter-state support seen in this war will probably remain as characteristic of future conflicts as they are for present ones. We thus need legal concepts for identifying who is 'at war' that capture the increasingly complex co-operation patterns of today's and tomorrow's wars. More widely, reflecting on party status may enhance our understanding of the architecture of the international legal regulation of armed conflict as a whole and its ability to respond to the realities of contemporary conflicts.
To prompt such reflection, this article, first, briefly explains why it matters, under current international law, whether a state is 'at war'. Although the legal meaning of party status today differs significantly from conceptions of the classical state of war that the current debates still evoke, party status arguably remains a central reference point for the international legal regulation of armed conflict. Building on that premise, the article, secondly, identifies the contours of a framework of legal criteria for establishing that a state has become a party to an ongoing international armed conflict (IAC)what would traditionally have been called a 'co-belligerent' and what we might label today a 'co-party'. As will be shown, two key criteria are decisive under this framework. The first criterion is that each potential (co-)party must make a contribution to the conflict that is of an operational character such that it is directly connected to harm caused to the adversary. The second criterion is that the contribution must be co-ordinated with fellow co-parties so that each coparty is involved in the decision-making processes regarding the co-ordinated military operations.  5 See, e.g., M. Schmitt, 'Are We at War?', Articles of War, 9 May 2022, available at www.lieber.westpoint.edu/are-we-at-war/. 6 Press Briefing by Press Secretary Jen Psaki, 3 March 2022, available at www.whitehouse.gov/briefing-room/press-briefings/ 2022/03/03/press-briefing-by-press-secretary-jen-psaki-march-3rd-2022/; M. Sermo, 'La cobelligérance, acte de guerre ou légitime défense collective ?', Le Monde, 26 May 2022, available at https://www.lemonde.fr/idees/article/2022/05/26/lacobelligerance-acte-de-guerre-ou-legitime-defense-collective_6127767_3232.html ( Although no intent to be a party is required, subjective dimensions of knowledge about the facts and circumstances constituting the co-ordinated contribution are inherent to these two criteria. To illustrate the distinctions that these criteria enable and how they can be operationalized, the article, in a third step, applies them to key support scenarios as exemplified in the Ukraine war. 2. The legal meaning of being 'at war' today In setting out how far they are willing to go in assisting Ukraine against Russia, several NATO member states officially attach their political red lines to the threshold at which they would be parties to the conflict under international law. 11 These references make the legal notion of party status a crucial security policy benchmark. 12 In doing so, the political discourse on Ukraine also hints at a particular legal conception of what being a party would mean. That conception is reminiscent of the 'classical' pre-Charter era implications of a 'state of war'. Traditionally, the state of war was envisaged as 'a legal condition in which it was entirely lawful for the two contending states to rain death and destruction upon one another'. 13 This legal notion is still at play when concerns are voiced that Western states becoming parties alongside Ukraine would entitle Russia to use force against Western states. 14 Today, however, even once states are parties to an armed conflict, every instance of force by and against them must still be assessed against the jus ad bellum prohibition of the use of force, in addition to the jus in bello. 15 A competing approach considers that between states that are parties to an international armed conflict, the legality of acts of force is no longer a matter for the jus ad bellum, but exclusively governed by the jus in bello. 16 That view is difficult to square with the basic structure of the prohibition of the use of force, which applies to individual acts. The prohibition does not make status-based distinctions along the traditional 'spheres' of peace and war. 17 Accordingly, where states are permitted to use force under the jus ad bellum, it may be lawful for them to perform acts that also make them parties. Put differently, states are not per se prohibited from becoming a party. Conversely, if a state is not entitled to use force against another state under the jus ad bellum, being engaged in an armed conflict with that state does not alter that conclusion. 18 Thus, Western states becoming a party alongside Ukraine would not entitle Russia 11 See note 6, supra.  to use force against those states since they could lawfully assist Ukraine in collective self-defence against Russia's armed attack. 19 At the same time, under the jus in bello, becoming a party would mean that members of the state's armed forces would be targetable as combatants. 20 The jus in bello legality of such targeting would not remedy the potential illegality under the jus ad bellum. 21 Still, in practice, the jus in bello assessment will likely shape operational decision-making since it offers more precise guidance for individuals on how to use force on the battlefield. 22 More widely, identifying whether a state is a party is crucial because the international legal regulation of armed conflicts 23 is, in many respects, organized by reference to whether the addressee of particular rules are parties or connected to parties. This is affirmed by the fact that parties to the conflict are referred to in hundreds of international treaty provisions and frequently addressed by international bodies such as the Security Council. 24 Parties bear central sets of international humanitarian law (IHL) obligations, under both the law on means and methods of warfare and the law relating to the protection of individuals. 25 In contrast to obligations, the relevance of rights traditionally attached to party status is doubtful today. Even if 'belligerent rights' (including establishing blockades, seizing contraband, or using force in reaction to breaches of neutrality law) are still affirmed by military manuals and operational practice, 26 they cannot grant permission for the use of force beyond the confines of the jus ad bellum. 27 At another level, party status also matters for the legal position of individuals. Accordingly, even as the 'humanization' and 'individualization' of international law in armed conflicts emphasize the increasing relevance of the individual within this body of law, 28 party status remains crucial for grasping how individuals are integrated into this legal system. Indeed, the nature of the connection of individuals to an IAC party influences which rules apply to them in the conduct of hostilities 29 as well as whether they fall into particular categories of persons protected by IHL. 30 This connection may also feed into establishing international criminal responsibility for specific war crimes that presuppose a specific connection of the individual to a party. 31 More subtly, the factors developed by international criminal jurisprudence for assessing the nexus requirement for war crimes all entail a specific connection between the perpetrator, victim, or relevant conduct and the parties. 32 In addition to the personal scope of obligations in armed conflict, identifying which states qualify as parties to an IAC is relevant to determining IHL's geographical scope. 33 Party identification is also crucial for applying neutrality law (which has traditionally governed the relations between parties to inter-state conflicts and third states, i.e., neutrals), 34 and the obligation of third states under Common Article 1 as well as customary international law to not provide aid, assistance, or encouragement to parties' IHL violations. 35 Beyond IHL, being a party can, for example, potentially modify how certain human rights obligations apply to that state, including the right to life and personal liberty and security. 36 It can also have implications for applying treaties such as the Montreux Convention -Turkey recently relied on this convention to restrict warship access to the Turkish straits during the Ukraine war 37which makes different provisions for the passage of warships through the straits 'in times of war' depending on whether Turkey is a 'belligerent'. 38 In sum, the importance of party status as a regulatory reference point for international law in armed conflicts suggests that having a clearer understanding of that concept helps one grasp the structure of this regulatory scheme as a whole. Accordingly, properly applying this regulation to an IAC such as the war against Ukraine requires knowing who is, and who is not, a party to that IAC. The stage for an account of the legal criteria for identifying parties is thus set.
3. The legal framework for identifying who is 'at war' International law presupposes that multiple states can be parties on the same side of an IAC. 39 At the same time, international law does not contain rules specifically developed for identifying parties.  One suggested solution has been to rely on the content of rules prohibiting specific co-operative acts with warring states, notably neutrality obligations to not provide assistance to parties and prevent them from using neutral territory, 40 at least if violations of such obligations are 'significant' and 'systematic'. 41 Yet, neutrality law violations and the termination of neutral status are best kept separate. 42 It is conceptually awkward to attach the termination of a status to the violation of an obligation that presupposes the persistence of that status. But more importantly, the very existence of the traditional enforcement measures for violations against a neutral state suggests that states retain their neutral status even after violating neutrality law. 43 Moreover, connecting party status to neutrality violations would raise questions regarding conduct that, prima facie, is inconsistent with neutrality but is carried out in support of the victim of an aggressor, in (collective) self-defence, covered by a Security Council mandate, or potentiallythough this last possibility remains controversialjustified as a third-party countermeasure under the law of state responsibility. 44 In such settings, neutrality obligations are arguably superseded such that they either do not apply at all or that violations of them are justified. At the same time, these considerations do not provide adequate distinctions regarding party status. This is because such distinctions would constrain the application of the jus in bello regarding states acting in conformity with the jus ad bellum. This would undermine the former's very raison d'être in an international legal order that prohibits recourse to force, but still has to regulate armed conflict.
Rather than relying on the content of neutrality law, the legal framework for identifying parties must be drawn from the system of the international legal regulation of armed conflict. The framework should reflect that parties are situated as the principal collective subjects in armed conflicts, bearing central sets of obligations regarding that conflict and determining the law applicable to individuals. Extending this status to actors that are only remotely connected to the conflict would distort this conception of centrality. Conversely, an overly narrow conception of party status could yield equally distorted results if collective actors who play a central role in a collaborative setting are not qualified as parties.
Based on an analysis of the structure of the international legal regulation of armed conflict, the remainder of this section sketches the elements of the legal framework for identifying parties in four steps. First, the direct connection to hostilities/military operations will be outlined, secondly, the co-ordination requirement, and thirdly, the subjective dimensions inherent in making a relevant co-ordinated contribution will be addressed. Fourthly, the temporal scope of party status will be clarified, i.e., when does it begin and end.

First criterion: Direct connection to hostilities
Traditionally, 'acts of war' were required for a third state to become a party to an ongoing conflict. 45 The contours of what this has meant have not received much attention. It is arguably not necessary for the acts of a (co-)party to meet separately the requirements that would suffice to create an armed conflict, as long as the acts of all (co-)parties, overall, meet these requirements. This point is particularly relevant for co-parties in non-international armed conflicts (NIACs), given the intensity threshold of 'protracted armed violence'. 46 Since this requirement relates to the conflict as a whole, it arguably needs not be met separately by each (co-)party. 47 Regarding inter-state conflicts, the notion of resorting to armed force between states, that gives rise to an IAC, 48 is not to be understood as an intensity threshold. 49 Nonetheless, it requires acts of a particular nature or quality. Certain acts that are regulated as hostilities/military operations as part of an ongoing IAC (such as preparatory or auxiliary acts to an actual resort to armed force 50 ) would not suffice separately to constitute an IAC in the first place. 51 Conceptually, there is no need to require that a state's conduct suffices to create a new IAC to become a party to a conflict that is ongoing.
Even if the legal criteria for the existence of an armed conflict and for identifying (co-)parties should therefore be distinguished, the conduct must be part of the hostilities or military operations that form the IAC. 52 Since hostilities/military operations constitute the conflict relationship between adverse parties on an ongoing basis, 53 by implication, international law presupposes that the contribution from each (co-)party consists, at a granular level, of acts constituting or forming part of military operations/hostilities. Hostilities/military operations are characterized as 'means or methods of injuring the enemy', 54 that is, 'acts which by their nature or purpose are intended to cause actual harm to the personnel and equipment of the armed forces'. 55 This notion covers a broader range of activities than 'attacks' (as defined in Article 49(1) AP I), 56 including non-violent activities preparing for 57 or supporting attacks. 58  conflict relationship between parties are relevant, and hostilities/military operations are narrower than 'the entire war effort'. 59 Against this background, the contribution's requisite character can be refined as demanding a relationship of 'directness' to harm to the adversary, as Greenwood and Upcher have hinted at in the context of IACs, 60 and the International Committee of the Red Cross (ICRC) in the context of NIACs. 61 To illustrate, regarding the 2003 Iraq invasion, the US considered that another state would not qualify as its 'co-belligerent' if its 'specific contribution ha [d] no direct nexus with belligerent or hostile activities'. 62 The US has later determined its co-party to be a state 'directly engaged with the US in hostilities or directly supporting hostilities against a common enemy' 63 (subsequently specified as 'direct operational support'). 64 Conversely, the perceived absence of such a direct connection was the basis for the Netherlands not to consider Kuwait a party to the Iran/Iraq conflict, despite Kuwait's wide-ranging military assistance to Iraq. 65 At the same time, no test for assessing this 'directness' of the operational connection in identifying co-parties has yet been established as a matter of international law. One practical way of assessment could be to ask whether the acts directly cause harm to the adversary in one step, or form an integral part of co-ordinated military operations that do so. This test would draw on the 'direct causation of harm' criterion advanced by the ICRC as a constitutive element of direct civilian participation in hostilities, 66 which has also informed the ICRC's 'support-based' approach to identifying parties to a pre-existing NIAC. 67 The first criterion has specified the conduct that allows for identifying a state as a co-party. The second criterion turns to the requisite character of the relationship between co-parties.

Second criterion: Co-ordination
To make a state a co-party, its operational contribution must be closely co-ordinated with one or more of the fellow co-parties. As the element that ties together co-operation partners' contributions, co-ordination sets the foundation for considering them as co-parties to the same armed conflict. Since one state can be simultaneously engaged in separate conflicts, fighting a common adversary is not all it takes to make multiple states co-parties. 68 By contrast, co-ordination 59 arguably makes a qualitative difference from the mere parallel fighting of a common enemy, and connects partners' acts such that they intertwine as contributions to one conflict. 69 In cases when more than two co-parties are on the same side of a conflict, it suffices for them to co-ordinate with one of the other states, if that state, in turn, co-ordinates with others. For example, states A, B, and C can be co-parties if states A and C do not directly co-ordinate but each only co-ordinate with state B. Accordingly, it is sufficient for all the contributions from co-parties to be connected through a link of co-ordination, even if some co-parties do not directly co-ordinate with some of the others.
Regarding the requisite degree of co-ordination, a helpful parameter is whether each co-party has a role in deciding how co-ordinated military operations are conducted. 70 Emphasizing involvement in the decision-making process is appropriate in light of the legal position that comes with being identified as a (co-)party. Indeed, it is the primary role of parties to ensure that the conflict is fought in accordance with IHL, 71 presupposing that parties determine how the conflict is conducted. This position relates to the conflict relationship with the adverse side, as a whole, which is constituted and shaped by the military operations of all co-parties. It, therefore, seems reasonable to require that co-parties be involved in the strategic, operational, and/or tactical decision-making that determines the (co-ordinated) military operations. This would be the case if partners co-ordinate their decisions to the extent that their contributions effectively build on one another.
To further specify the elements outlined so far, a crucial question remains as to what extent these elements also have subjective dimensions.

Subjective dimensions
When the above elements are met, party status is an automatic legal consequence, independent of whether parties intend, know, or accept that consequence. On subjective conceptions of the 'state of war', belligerent status depended on states' intent to be at war. 72 Such conceptions can no longer be reconciled with the basic premise that the application of the contemporary international legal regulation of armed conflict does not depend on whether states want it to apply in a given case. 73 Nonetheless, a certain mindset regarding the facts and circumstances constituting the relevant co-ordinated contributionnot the ensuing status consequenceis inherent to the two elements. Knowledge is a plausible candidate for these subjective dimensions. Requirement of activities with a direct connection to harm in sufficiently close co-ordination with one's partners cannot be considered fulfilled when the respective state is unaware of what it is doing, for example as the result of an error or being misled. 74 In practice, the requisite awareness will usually be inferred objectively from the factual patterns, 75 unless it is explicitly externally manifested, for example in official statements or documents. 69 Having developed elements to identify a state as a (co-)party, a final necessary specification pertains to the extension of this status in time. When does it begin and when does it end?

Temporal scope of party status
A state's (co-)party status to a pre-existing IAC begins as soon as it has made a sufficiently coordinated contribution of the requisite character, as specified above. For contributions consisting of recurrent acts, some repetition may be helpful evidence in establishing that a contribution meets the requirements. 76 Party status ends with the end of a conflict, but in practice this can be difficult to pin down. 77 Conversely, even during an armed conflict, an individual state's co-party status may end once its activities no longer meet the requirements for identifying it as a party in the first place. Conceptually, this analysis is simply a reversal of establishing the inception of party status. 78 It would thus not be necessary for a state to disengage fully from a conflict and stop its co-ordinated contribution entirely, as others have suggested. 79 A change in the quality of the contribution (such that it no longer meets the requirements) would already mean that the respective state can no longer be considered a party. Nonetheless, it seems reasonable, in practice, to presume that a state remains a co-party until that presumption is rebutted. The presumption would be rebutted by an externally discernible manifestation of a significant change of the contribution or its cessation. A changed pattern over a prolonged period can be helpful evidence. This would avoid the legal uncertainty that could otherwise result from 'revolving door' situations or simply from the fact that the relevant changes may not be instantly evident to other actors that need to make the assessment in the context of ongoing operations. 80 Finally, the end of a state's party status does not necessarily mean no further legal consequences will flow from this status. The point in time at which a state must have been a party is to be carefully discerned by interpreting the specific rule that attaches legal consequences to party status. While obligations relating to the conduct of hostilities will typically not apply to a former party once it ceases to be a party, 81 many obligations regarding protected individuals will extend beyond this point in time. Some obligations that are activated while a state is a party will still need to be discharged after its party status ends. For example, a former party's obligations to care for a wounded individual do not simply end because it ceases to be a party. 82 Other obligations may even be activated after the cessation of hostilities but still entail consequences for former 76 See Ferraro, 'Applicability', supra note 61, at 586. parties, such as obligations to search for and collect the dead and account for the missing, 83 obligations relating to persons deprived of their liberty, 84 or obligations to take measures regarding explosive remnants of war. 85 4. Operationalizing the legal framework in and beyond the war in Ukraine To illustrate how this account of the legal criteria for identifying parties may operate practically, it is helpful to consider the key forms of military assistance that different states have provided to Ukraine and Russia in the current war: weapons and training, intelligence, cyber support, and allowance for the use of territory. 86 We will see that the suggested legal criteria permit reasonable distinctions that may also resonate with the legal lines that states themselves seem to draw in this war and with a view to future conflicts.

Weapons and training
Supplying arms to Ukraine does not establish a sufficiently direct connection to hostilities, since only the actual use of the weapons causes harm to Russia. For this assessment, it does not matter what kind of weapons or materials are supplied, or whether Ukrainian soldiers are additionally trained on those weapons. 87 Repeated affirmations from Western states that such assistance has not made them parties 88 are therefore in line with the legal framework outlined above. The matter would be different if military advisors participated in the planning of concrete military operations. Such participation could both possess the requisite direct connection to hostilities and attest to a role in the decision-making processes, thus satisfying the co-ordination requirement.

Intelligence
The case of specific patterns of intelligence co-operation may be different than that of weapons transfers. 89 The US and other NATO states, for example, apparently upload intelligence to a portal that Ukraine can access in real-time. 90 Reportedly, such intelligence has included data on the location of specific targets, either confirming requested target locations or pointing to new potential 83 See, e.g., GC I, supra note 30, at, Art. 15; GC II, supra note 30, Art. 18; GC IV, supra note 30, Art. 16; AP I, supra note 18, Art. 33(1); ICRC CIHL Study, supra note 20, rules 112-17. 84 On the temporal scope of such obligations see GC III, supra note 30, Art. 5. 85 Arts. For an assessment at an early stage of the conflict see A. Wentker, 'At War: When Do States Supporting Ukraine or Russia become Parties to the Conflict and What Would that Mean?', EJIL:Talk!, 14 March 2022, available at www.ejiltalk.org/at-warwhen-do-states-supporting-ukraine-or-russia-become-parties-to-the-conflict-and-what-would-that-mean/. 87 The same is true regarding the supply of drones to Russia by Iran and the reported provision of training and maintenance on these drones by Iranian advisors in Crimea, see C. Vinograd, 'Iran's Foreign Minister Acknowledges that Drones Were Sent to Russia, but Says it Happened before the War.', New York Times, 5 November 2022, available at www.nytimes.com/2022/11/ 05/world/europe/irans-foreign-minister-acknowledges-that-drones-were-sent-to-russia-but-says-it-happened-before-thewar.html?searchResultPosition = 1; J. Borger and D. Sabbagh, 'Iran Provides "Technical Support" for Russian Drones Killing Civilians, Says US', Guardian, 20 October 2022, available at www.theguardian.com/world/2022/oct/20/russia-ukraine-wariran-drones-advisers-crimea. 88 See note 6, supra. 89 See also Schmitt, supra note 5. 90 N. Bertrand and K. Lillis, 'US Officials Say Biden Administration is Sharing Intelligence with Ukraine at a "Frenetic" Pace after Republicans Criticize Efforts', CNN, 4 March 2022, available at www.edition.cnn.com/2022/03/04/politics/us-ukraineintelligence/index.html; for reports of targeting intelligence provided to Ukraine by Germany's Federal Intelligence Service, albeit not in real-time, see H. Stark, 'Hilfe, die zum Ziel führt', Zeit, 28 September 2022, available at www.zeit.de/2022/40/ ukraine-russland-krieg-bnd-geheimdienstinformationen. targets, enabling Ukraine, for example, to take out several Russian generals and the missile cruiser 'Moskva'. 91 Conversely, US intelligence on specific imminent strikes by Russia has reportedly helped Ukraine evade them. 92 Target geo-localization and verification are part of the targeting process and thus a prime example of a military operation that directly harms the adversary. The reported patterns of intelligence co-operation also display close-knit co-ordination. US intelligence has been integrated into Ukrainian military operations such that the US has a significant involvement in key aspects of the decision-making. Reports also indicate that the US was aware that its intelligence contribution was part of operations directly harming Russia and that it had a role in the decision-making on these operations. 93 Based on these reports, there seems to be a good case for considering the conditions of co-party status fulfilled. The facts can, of course, not be fully ascertained, and the US contends that it did not share intelligence that was sufficiently granular 'explicitly to target and kill Russian soldiers'. 94 Implicitly, however, this factual line of defence may indicate that the US considers that such acts could indeed push states closer to the line of becoming a party as a matter of law. 95 Based on a similar reasoning, Russian officials concluded that through 'the aid of American intelligence forces' to Ukraine, 'Washington is essentially coordinating and developing military operations, thereby directly participating in military actions against our country'. 96 Both the US' and Russia's position suggest that providing targeting intelligence can, in certain circumstances, make a state a co-party. In doing so, both positions hint at criteria that resonate with the legal framework criteria set out above.

Cyber support
For the reported US cyber support to Ukraine, the Commander of US Cyber Command acknowledged that the US was conducting cyber operations 'across the full spectrum', including 'offensive' operations to assist Ukraine. 97 The general did not, however, provide details on the exact nature of the US cyber support and its relationship to Ukraine's cyber operations. Accordingly, a sufficient operational connection is conceivable, though not publicly known. 98 Depending on the factual setup, this may either be because the support as such constitutes military operations that directly cause harm, or because it is integrated into kinetic military operations that do so. 99 Whether there has been sufficiently close co-ordination between cyber support and Ukraine's military operations is again, not publicly known, but it is certainly imaginable. In principle, therefore, cyber support seems to be capable of meeting the legal criteria for a state providing such support to be become a co-party. 91