This chapter explains how international law identifies co-parties to armed conflict.
Being a party to an armed conflict entails significant legal implications. (These implications are discussed further in Chapter 3.) It matters that we know when states, international organizations or armed groups cross the line to become a party to an armed conflict. Establishing the answer to that question is particularly challenging when there are multiple potential parties on the same side – that is, co-parties to armed conflict.
Traditionally, states fighting on the same side of a war have been referred to as ‘co-belligerents’. This paper, instead, refers to multiple parties on the same side of an armed conflict as ‘co-parties’. This change is intended to reflect the wider shift in international legal terminology from ‘war’ and ‘belligerents’ to ‘armed conflict’ and ‘parties to the conflict’. To be clear, the term ‘co-party’ simply means being a party to an armed conflict – either international or non-international – alongside other parties on the same side. It is not a separate status to that of a party. All the legal implications of party status set out in Chapter 3 apply equally to co-parties.
The question of identifying co-parties can arise in relation to various forms of cooperation in IACs or NIACs involving states, international organizations and/or non-state armed groups. There is one setting, however, in which such issues cannot arise. This is the scenario in which a state supports a non-state armed group in a conflict with another state. Here, if the supporting state were to become a party, the conflict between the two states could only be an IAC (provided the requirements for the existence of an IAC between the two states are met). The armed group, however, cannot be party to that IAC in its own right (as seen in Section 1.2) – if it is to remain a party on its own (and not simply form part of one of the states parties to the IAC), the armed group can only be a party to a separate NIAC against the adverse state. In such a scenario, there may be multiple parallel, but separate conflicts, but not multiple co-parties on one side of the same conflict.
This chapter develops an account of the legal framework for identifying who is a co-party to an armed conflict, as follows. First, methodological questions are addressed and the field of potential starting points and existing approaches to the issue charted briefly. Second, based on these considerations, legal criteria for identifying co-parties are sketched out and their practical operation is illustrated. Finally, the temporal scope of co-party status is analysed – that is, when co-party status begins and ends.
2.1 Methodology, related concepts and existing approaches
International law presupposes that there can be multiple parties on the same side of an armed conflict. But, at the same time, no rules of international law have been developed specifically to establish when that is the case. Neither treaty law nor customary international law explicitly provides criteria for determining co-party status. Therefore, rules must be drawn from the legal framework of international law in armed conflict and in light of state practice in past and current conflicts. The task in establishing criteria is thus to draw out what international treaty and customary rules presuppose, when they refer to parties to a conflict, about what has made the respective collective entity a party.
Methodologically, this task involves interpreting the relevant treaty provisions and establishing the content of customary international law rules. Interpreting treaty provisions usually begins with the ‘ordinary meaning’ of the terms of the relevant provisions. However, the identification of co-parties does not flow from the ‘ordinary meaning’ of the term ‘parties to an armed conflict’. Legal criteria for identifying co-parties may, instead, be drawn from other means of interpretation, namely from an interpretation that considers the ‘context’, as well as the ‘object and purpose’, of the terms. Contextual – or systematic – interpretation, specifically, are crucial.
State practice can also help with interpreting treaties. Relevant incidents of practice may be considered as supplementary means of interpretation. The practice of states and international organizations may also inform our understanding of the relevant customary international law rules. In sum, both the system of the law regulating armed conflict and international practice must be considered in coming to conclusions on criteria for identifying co-parties. The concepts of armed conflict are a natural place to start.
The relationship between the concepts of armed conflict and the identification of parties
Historically, the concept of war was either understood in subjective terms – i.e. as dependent on states’ intention to be at war, chiefly when expressed formally in declarations of war – or in objective, material terms as armed confrontations of a certain scale. The latter conception of war, as defined through facts on the ground, is closer to present concepts of armed conflict. At the same time, a relic of subjective, formal concepts of war today is that declarations of war arguably remain possible between states. Indeed, Common Article 2 to the Geneva Conventions I-IV still provides that ‘the present Convention shall apply to all cases of declared war or any other armed conflict’. Declarations of war thus present a theoretical way to co-party status in inter-state conflict (even if this might today constitute a prohibited threat of force), but they have long become rare in practice. Because of the scarcity of such declarations, it should not be lightly assumed that states intend to declare war. Accordingly, an explicit statement to that effect should be required of any such state.
Today, IACs and NIACs – as defined in Section 1.2 of this paper – are the prevalent concepts in the legal regulation of war: both are characterized as factual situations of conflict (leaving aside the possibility of declared wars between states). In bilateral conflict settings, establishing that an IAC or NIAC exists and establishing that the two collective entities involved are parties to the conflict will generally be one and the same exercise. When the bilateral confrontation between two collective entities – states, international organizations or non-state armed groups – meets the requirements for the existence of either an IAC or NIAC, these two will be parties to an IAC or NIAC, respectively.
It is clear that the criteria for the existence of an IAC or NIAC must be met for there to be any party to the conflict. Less clear, however, is whether every co-party must meet these criteria separately in its conflict relationship with the other side in order to become a co-party.
Declarations of war present a theoretical way to co-party status in inter-state conflict, but they have long since become rare in practice.
The question may become relevant in the following two scenarios outlined below and to which this paper later refers. In the first scenario, party A and party B are already engaged in an armed conflict, when a potential party C joins that conflict on A’s side. If the confrontation between A and B meets the criteria for the existence of an IAC or NIAC, does the same also need to be true of the confrontation between C and B, to establish that C has become A’s co-party? In the second, the confrontation between (potential) parties A and C, on the one hand, and (potential) party B, on the other hand, meets the criteria for an armed conflict if A and C’s action is taken together. Viewed in isolation, however, neither the confrontation between A and B, nor that between C and B, would suffice to create an armed conflict. Scenario 2 is mostly relevant in NIACs – namely if the requisite degree of intensity of armed violence is only reached jointly by A and C in regard to B. Since, on a widespread view, there is no intensity threshold for an IAC to exist or, at most, a low one, it is hard to think of cases where the acts of parties A and C must be considered jointly to establish that there is a resort to armed force in regard to party B. Scenario 1-type situations may, however, also arise in IACs. Even if no intensity threshold must be met in IACs, acts of a particular nature or quality are required to qualify as a resort to armed force that triggers an IAC. Not all acts that would form part of hostilities if carried out during an IAC would necessarily be sufficient to trigger an IAC in and of themselves – for example, the provision of targeting intelligence for an airstrike against another state.
State practice and decisions by international courts and tribunals appear to point against assessing separately for each co-party whether its actions constitute an armed conflict with the adverse party. Neither states nor international courts and tribunals refer to the criteria for the existence of an IAC or NIAC when identifying co-parties, with practice instead taking (explicitly or implicitly) the contributions by multiple parties together when assessing whether an armed conflict exists. For example, during the 2003 Iraq war, the US considered Kuwait and Qatar as its co-parties in the IAC against Iraq, even though these two states had not resorted to armed force themselves – unlike the other states that the US considered as its co-parties – but had notably, among other things, allowed their territory to be used for US attacks on Iraq. In Bemba, the ICC considered armed groups and the CAR government as co-parties to the same NIAC with other armed groups, without conducting a separate assessment of the intensity threshold – which the activities of the CAR government may not have met if considered on their own. Similarly, the ICC did not carry out separate intensity assessments to find several armed groups to be co-parties in Katanga and Ntaganda. Importantly, however, the requisite degree of organization was assessed separately for each co-party in the latter cases.
Conceptually, there does not seem to be a need for requiring a separate assessment in either of the two scenarios outlined above. Regarding scenario 1 – i.e. where an armed conflict already exists – it seems strange to require that a potential co-party must carry out acts that would suffice to create a new armed conflict in order to become a party to an armed conflict that already exists. Regarding scenario 2 – i.e. where an armed conflict is jointly created – it is difficult to see why the same factual result (i.e. intense armed violence on the ground) should be treated differently merely because that result is reached by way of a division of labour between multiple entities. Structurally, both the requirement of resort to armed force in IAC and protracted armed violence in NIAC regard the nature of the conflict as a whole. It is therefore sufficient to require that these criteria must be met overall by all co-parties in their confrontation with the adverse side. In addition to being conceptually unnecessary, attempts to distinguish the action of multiple co-operating partners may also be difficult in practice.
There are concerns that this conclusion risks lowering the threshold for the application of IHL, particularly in NIACs – with the effect that the more permissive IHL rules of targeting reduce human rights protection for the affected individuals. Such concerns must still be taken seriously, but can potentially be accommodated by formulating strict criteria for when actions by different (potential) co-parties may be assessed together.
More widely, Section 3 shows that legal consequences of identifying parties go beyond targeting implications under IHL. The effect of imposing IHL obligations on an entity once it becomes a party to conflict, or the legal implications for establishing international criminal responsibility, may lead to an overall more nuanced picture than an exclusive focus on the above targeting implications. This is all the more significant, as insisting on separate assessments carries the same risks. Notably, there may be a temptation to read down the intensity assessment in cooperation settings when carrying out a separate intensity assessment for each co-party, particularly given the practical difficulties involved in such a separate assessment. That temptation may ultimately lead to an even more extensive – and unfettered – application of IHL, to the detriment of human rights protection.
In sum, therefore, the conflict-related criteria for the existence of an IAC or NIAC, respectively, (i.e., ‘recourse to armed force between States’ in IACs and meeting the threshold for intensity of hostilities in NIACs) must only be met overall, considering the contributions by all co-parties jointly. By contrast, the party-related criteria for the existence of an IAC or NIAC (i.e. statehood in IACs and sufficient organization in NIACs) must be met separately by each co-party. As noted in the introduction to this paper, these party-related criteria are basic prerequisites for any party to either an IAC or NIAC.
Whether an aggregated assessment is accepted or not, additional legal criteria are needed for establishing that multiple states or armed groups are parties to the same armed conflict (i.e. co-parties), and not parties to separate armed conflicts. To be clear, these additional criteria will necessarily need to be met by each co-party on its own. Distinguishing parties to the same armed conflict from parties to separate armed conflicts matters for several reasons. First, in both IACs and NIACs, the legal implications of party status (naturally) only apply regarding the conflict to which the particular entity is a party. In particular, there arguably are duties between co-parties, flowing from their party status. Additionally, in IACs, the relationship between states that are parties to separate armed conflicts would be regulated by the law of neutrality.
Accordingly, the criteria for the existence of an IAC or NIAC are important parameters in identifying parties – they must necessarily be met (at least overall) – but they do not give a complete answer to the question of how to identify co-parties.
Relationship to (breaches of) neutrality obligations and ius ad bellum standards
International law traditionally recognized two, mutually exclusive statuses in war – a state was either a party or a neutral. Neutral states owed certain duties of prevention and abstention to the parties to the conflict. Scholars have sometimes suggested that there is a necessary relationship between compliance with the law of neutrality and retention of neutral status, such that a neutral state might lose that status and become a co-party to an international armed conflict where they systematically or significantly violate their obligations under the law of neutrality.
Curtis Bradley and Jack Goldsmith applied this interpretation of the law of neutrality – which applies in inter-state conflicts – by analogy to define the scope of the US’s domestic law authorization to use force against non-state armed groups under the 2001 US Authorization for the Use of Military Force (AUMF), arguing that this scope extended beyond those groups responsible for the 9/11 attacks to include ‘co-belligerents’. While highly controversial, this reading of the law of neutrality, and the approach of defining the scope of its authority under the AUMF by analogy to that law, has found some support in US government and judicial practice in US domestic litigation, in the context of establishing that an armed group is an ‘associated force’ of the groups responsible for 9/11. On this account, an ‘associated force’ must first ‘be an organized, armed group that has entered the fight alongside Al-Qaeda or the Taliban. Second, the group must be a co-belligerent with Al-Qaeda or the Taliban in hostilities against the US or its coalition partners’ and ‘a co-belligerent with Al-Qaeda or the Taliban in hostilities against the United States or its coalition partners.’
The extent to which the pre-1945 dichotomy in international law between party and neutral status has survived the UN Charter is not entirely settled, given that the UN Charter (and custom) now establish generally applicable rules governing when armed force is lawful, together with the collective security system.
Assuming that the law of neutrality continues to exist to some degree, modified by the UN Charter framework in particular circumstances, it is clear from practice and scholarship that there is no necessary relationship between compliance with the law of neutrality and party status. Despite carrying consequences under the law on state responsibility, violations of the law of neutrality (even significant or systematic violations), such as providing a party with continuous financial support or access to the neutral state’s airspace have not hitherto been considered to lead to a loss of neutral status and the acquisition of co-party status by the violating state.
During the Iran–Iraq war of 1980–88, for example, the various states supporting Iraq in violation of neutrality law were not considered to be co-parties to the conflict. For example, Kuwait, which was reported to have allowed its airspace to be used by Iraqi combat aircraft and extended logistical and financial support to Iraq, was not considered a co-party by states other than Iran (which appeared to do so not as a consequence of Kuwait violating its neutrality obligations, but rather because of the extent of Kuwait’s involvement in the conflict). Similarly, following the 2003 invasion of Iraq by US-led coalition forces, many European states (including Germany and Italy) assisted and permitted use of their territories by the coalition states without themselves being considered parties to the conflict.
The object and purpose of the law of neutrality was to contain hostilities. It is consistent with this purpose that violations of one’s obligations as a neutral, even if substantial or systematic, do not as such lead to a loss of neutral status and the acquisition of party status. This purpose would clearly be frustrated if a consequence of violating that law was the extension of hostilities to the violating state. In consequence, the content of the law of neutrality cannot, as a matter of law, provide the criteria for determining party status.
The object and purpose of the law of neutrality was to contain hostilities. It is consistent with this purpose that violations of one’s obligations as a neutral, even if substantial or systematic, do not as such lead to a loss of neutral status and the acquisition of party status.
In addition to violating the law of neutrality, providing assistance to a state party to an armed conflict may also engage international law rules on complicity. As a general matter, the breach by an assisting state of a complicity rule does not affect whether or not it is a party. For example, the fact that an assisting state’s authorization of the transfer of weapons breaches Article 6(3) of the Arms Trade Treaty does not mean that it becomes a party to the conflict. Rather, this is considered as a discrete breach of international law. Similarly, a state’s breach of the rule on aid or assistance in Article 16 of the Articles on State Responsibility (ASR) does not itself make the assisting state a party to the conflict.
The same must also apply insofar as the military assistance attracts the ius ad bellum. The ius ad bellum is that body of international law that governs the legality of the use of force by one state against another. If a state provides assistance to another state that uses force, that assistance may in certain circumstances itself constitute a use of force as a matter of the ius ad bellum under Article 2(4) of the UN Charter and customary international law. It might be argued that once the acts of a state providing assistance cross the threshold of ‘force’ against another state under the ius ad bellum, the assisting state would become a co-party to an IAC that is occurring between the state receiving the support and the adverse state. Under this argument, the question of when assistance constitutes a use of force and party status would be based on the same standard. However, there are no indications in international practice that such a connection is drawn. The debates on ‘indirect uses of force’ and party status are separate discourses both in practice and scholarship. It is also doubtful how much would be gained from making such a connection, since the ius ad bellum issues in question are perhaps no less contested and unsettled. Finally, it should be noted that the ius ad bellum question here is whether there is a separate use of force. Ius ad bellum standards could thus conceivably help to find that a separate IAC exists. They do not seem to be particularly helpful to discern when states become co-parties to the same, rather than to separate, armed conflicts.
There is one, specific, potential complication to this general rule that ius ad bellum standards do not determine whether a state is a party to the underlying conflict – Article 3(f) of the Definition of Aggression of 1974, which qualifies as an act of aggression:
The complication follows from the phrasing. This distinctive form of complicity – making available territory to an aggressor – is itself qualified as an ‘act of aggression’. It may seem intuitive that an act of aggression will also make the assisting state a party, and specifically a co-party to the underlying conflict. But there does not seem to be practice that specifically makes the connection between the conduct under Article 3(f) and becoming a (co-)party to the underlying conflict.
The ICRC’s ‘support-based approach’
To establish when states or international organizations assisting states that are parties to an ongoing NIAC themselves become parties to that NIAC, the International Committee of the Red Cross (ICRC) has proposed what it labels the ‘support-based approach’. The support-based approach requires the following criteria to be met cumulatively:
The ICRC has extended this approach beyond its initial scope to support provided to non-state armed groups fighting other armed groups, and to support provided by non-state armed groups in NIACs. Regarding ‘coalitions’ of armed groups, the ICRC has suggested that these could be deemed parties to the same NIAC if they ‘display a form of coordination and cooperation’, provided that ‘the sum of the military actions carried out by all of them fighting together’ meets the intensity threshold. Some aspects of the ICRC’s approach and its underlying structural considerations can usefully be drawn on in setting out an overarching legal framework for identifying co-parties in both IACs and NIACs.
2.2 The legal criteria for identifying co-parties
This section outlines the legal criteria for identifying co-parties. Two preliminary points are necessary.
First, the account put forward here builds on the previous sections of this paper. It thus presupposes that each co-party meets the ‘party-related’ criteria flowing from concepts of IAC and NIAC. That is, the criteria related to the nature and structure of the entity itself – i.e. statehood in IACs (with the exceptions noted in Section 1.2) and sufficient organization in NIACs. The account also presupposes that the ‘conflict-related’ criteria for the existence of an IAC or NIAC are met overall – i.e. resort to armed force for an IAC and protracted armed violence for a NIAC. In addition, the account focuses solely on how states, international organizations or non-state armed groups can become co-parties by virtue of their acts. The theoretical possibility for states to become co-parties by declaring war is excluded for the purposes of the paper.
Second, saying that a collective entity ‘acts’ as a matter of international law presupposes that acts of individuals can be attributed to that collective entity. There may be complex questions of attribution in establishing that a state, international organization or non-state armed group has become a (co)-party, particularly when these actors operate in ‘coalitions’ of different sorts. These problems, however, are not specific to identifying co-parties and will therefore not be further considered here. Indeed, attribution of individual acts to the relevant collective entities is also presupposed when establishing that an armed conflict exists.
Provided that these baseline requirements are satisfied, two legal criteria must cumulatively be fulfilled to establish that a state, an international organization or a non-state armed group becomes a party to an armed conflict, whether this is a conflict that is already ongoing or just being initiated, and whether this is an IAC or a NIAC.
First, the acts of the respective state, international organization or non-state armed group must possess a direct connection to hostilities. Second, there must be some degree of cooperation or coordination with at least one other co-party against a common adversary. The rationale for each of these criteria and how they can be assessed will briefly be explained in turn. Thereafter, any subjective dimensions of these criteria will be discussed. Practical examples of support scenarios in armed conflict will be considered to illustrate how the criteria proposed in this section operate in practice.
Criterion 1: Direct connection to hostilities
At their core, armed conflicts – whether international or non-international – consist of hostilities. These are the acts that parties perform against each other, and therefore constitute the essence and the most granular components of the conflict relationship between adverse parties. The notion of hostilities is broader than that of ‘attacks’ in the sense of Article 49(1) AP I (‘acts of violence against the adversary, whether in offence or in defence’) and also includes acts preparing or supporting attacks. At the same time, the concept of hostilities is narrower than ‘the entire war effort’. Hostilities can thus be defined as the means and methods of causing harm to the adversary. Since hostilities make up the conflict relationship between parties, all co-parties must have a specific connection to the hostilities. That connection should be understood as one of ‘directness’.
Requiring such a direct connection to hostilities is not only sound in light of the foregoing considerations as to the structure of the international legal regulation of armed conflict. The requirement also resonates with how states have drawn the line of co-party status in their practice. Regarding IACs, for example, reference can be made to the US’s position that it would not consider other states as its ‘co-belligerents’ against Iraq absent such a direct connection. The Netherlands reasoned similarly to conclude that Kuwait had not become a co-party to Iraq in the Iran–Iraq war, in which Kuwait supported Iraq by various means. More recently, Russia based its claims that the US had become a co-party of Ukraine in the latter’s conflict with Russia partly on the notion that the US ‘essentially coordinates and develops military operations, thereby directly participating in the hostilities’ against Russia and was ‘directly involved in the conflict’. Regarding the NIAC with Islamic State, Denmark referred to similarly worded considerations to assess whether it was a party to that NIAC, as well as more generally whether it was a co-party to an IAC or NIAC by virtue of its involvement alongside other partners.
To assess whether a sufficiently direct connection to hostilities exists, a range of factors may be considered without being in themselves determinative of co-party status. These factors include the nature and scale of the activities performed, and their geographical and temporal proximity to harm caused to the adversary.
Criterion 2: Cooperation or coordination
Criterion 1 relates to the character of a co-party’s conduct. Criterion 2, which must be fulfilled cumulatively with the first, concerns the relationship between co-parties.
In addition to a direct connection to hostilities, the relationship between multiple co-parties must be such as to warrant treating them as parties to the same armed conflict. Parallel fighting against a common enemy would be insufficient, as this could simply involve separate armed conflicts against the same enemy. To tie the acts of multiple states or other collective entities together so that they become co-parties, there must be some degree of cooperation or coordination of their activities against a common adversary regarding the specific hostilities, so that they effectively build on one another as part of one armed conflict. More specifically, each co-party must cooperate or coordinate with at least one other co-party on the same side of the conflict. It is not necessary that all co-parties on one side cooperate or coordinate with each of the others for there to be a sufficient link of cooperation connecting them.
The exact degree of cooperation or coordination required cannot be delineated in the abstract. Here again, certain non-determinative considerations can be used in practice to assess the degree of cooperation. These considerations include the geographical and temporal proximity of one’s own activities to one’s partners’ activities, and the existence of institutionalized structures for coordinating one’s activities. For example, where states delegate ‘operational command’ and/or ‘operational control’ (in NATO terminology) in the context of multinational forces, that will be sufficient cooperation or coordination in practice.
Subjective dimensions
Whether a state or other collective entity is a co-party to an armed conflict does not depend on whether a state (or other potential party) wants to be a co-party. The point is important. States or other potential co-parties do not need to specifically intend their own co-party status and the legal consequences attached to that status. It is the object and purpose of the current international legal framework regulating armed conflict – for which party status is a crucial reference point – that these rules apply when the facts on the ground so require. Accordingly, attempts to identify who is a party must be based on an objective assessment of the relevant facts.
At the same time, fulfilling the two criteria proposed in this paper presupposes that the respective state, international organization or armed group acts with knowledge of the relevant facts. As has been noted, this is particularly true of the cooperation or coordination requirement. Cooperating or coordinating with respect to specific hostilities presupposes an awareness by the state or armed group of the factual context in which its activities are embedded, and thus some degree of knowledge of the circumstances surrounding its partners’ activities. If its activities consist of providing military assistance to partners, the two criteria advanced here for co-party status presuppose that the provider of the assistance knows how the assistance is used. This would not be the case if the provider has been misled or errs about these facts. In that sense, an element of knowledge is inherent to the criteria for identifying co-parties. Crucially, however, this subjective element relates only to the underlying facts, not the ensuing legal consequences in terms of party status. In practice, evidence for the requisite knowledge will usually have to be drawn from the factual circumstances surrounding the potential co-party’s acts, unless it is clear from official statements or documents.
It should be acknowledged, however, that whether a state considers itself or another state a co-party to a particular armed conflict will play a role in practice. While not legally determinative, states can hardly ignore the political implications of an opinion on party status voiced publicly by another state. For example, if a state considers other states that support its adversary as the adversary’s co-parties, that claim does not, in and of itself, affect whether they actually are co-parties as a matter of law in that situation. At the same time, the respective states will certainly consider such statements in deciding their further course of action. To be in a position to counter false claims of co-party status – and prevent them from affecting the development of the legal rules on this point – states need to be aware of the legal criteria for establishing that status.
Practical examples
To illustrate how the account set out in this paper operates in practice, it is helpful to consider some hypothetical examples.
On one end of the spectrum, joint airstrikes by combat aircraft from multiple states against a common adversary clearly bear out the requisite direct connection to hostilities and presuppose sufficiently close cooperation and coordination to make these states co-parties. The same would be true of joint ballistic attacks by multiple armed groups against a particular target of an adverse state.
On the other end of the spectrum, there are certain activities in support of a party to a conflict that could not conceivably meet the criteria for co-party status. For example, providing financial or political assistance to other states, international organizations or armed groups does not constitute a sufficiently direct connection to hostilities. Provision of humanitarian assistance of any kind is even less sufficient. General supply of weapons or other military materiel still lacks a direct connection to specific hostilities – understood as acts harming the adversary – since it is only the actual use of weapons that harms the adversary.
For other activities, the context in which they are taking place will be paramount. Facilitating the acquisition of general capabilities does not constitute a sufficiently direct connection to any specific hostilities. Examples include providing general combat training to soldiers of another state or fighters of an armed group or training designed to teach soldiers or fighters how to use weapons systems. In both cases, it is only the implementation of these skills on the battlefield that causes harm. By contrast, if military advisers of one state assist in the planning of specific military operations by another state, to the point that both states are involved in the decision-making process for specific operations in the conduct of hostilities, there can be both a sufficiently direct connection to hostilities and a sufficient degree of cooperation and coordination.
Similarly, logistical support often does not suffice to meet the criteria for co-party status, though it may do so in specific contexts. For example, transporting military equipment from one military base to another, or providing air-to-air refuelling for such transport, do not suffice. Transporting the troops of another state to the front line or providing air-to-air refuelling to combat aircraft as part of specific military operations in the conduct of hostilities could, however, have a sufficiently direct connection, and would also involve a sufficient degree of cooperation or coordination.
Context also matters regarding the provision of intelligence. Routine provision of intelligence to another state – for example, under a standing agreement – will not make the state providing the intelligence a co-party. Even if intelligence is provided that can be militarily helpful – for example, in assessing the adversary’s capabilities – that would not suffice. The matter may be different if intelligence on specific military targets is provided. Geo-locating and verifying a target are part of the targeting cycle and thus of a military operation against that target. The same would be true of intelligence that enables a partner to disrupt such a specific targeting operation by the adversary. Both scenarios would constitute a direct connection to hostilities, and involve significant cooperation or coordination between the provider and the recipient. Whether intelligence is provided to a partner in real-time, rather than in longer intervals, may be a helpful consideration in establishing a sufficiently direct connection to hostilities and close cooperation or coordination between partners, but alone it is neither sufficient nor necessary.
For cyber support, similar distinctions can be drawn. Merely enhancing the general cyber capabilities of another state, international organization or armed group would not suffice for co-party status. Cyber operations can, however, either be integrated into specific kinetic military operations of the recipient of assistance or by themselves constitute operations that harm the adversary and thus form part of hostilities. In the latter case, whether or not the state, international organization or armed group conducting the cyber operation would become a co-party would depend on whether they cooperate or coordinate with the recipient of such cyber support. Cyber operations launched against a common adversary without any cooperation could only constitute a separate armed conflict, provided the criteria for creating an IAC or NIAC with that adversary are met.
Again, when states allow their territory to be used by other states, international organizations or armed groups, different scenarios must be distinguished. When states allow overflights through their airspace, or even stopovers for carrier or combat aircraft on the way to the front line, this does not make them co-parties with any state that they allow to use their territory. By contrast, when a state allows its territory to be used as a launchpad for specific hostilities against another state or armed group, this may constitute a sufficient connection to the hostilities. The cooperation or coordination requirement is also relevant to this example. If a state uses another state’s territory without at all involving that other state – perhaps even without that state being aware that its territory is being used or what it is being used for – the territorial state would not become a party, even if hostilities are launched from its territory.
2.3 Temporal scope of co-party status
In principle, an entity becomes a co-party when its actions meet the criteria developed above. The first acts taken in relation to an armed conflict may suffice. In practice, however, some repetition will be helpful evidence to establish co-party status, for example, through recurrent air strikes or the regular provision of targeting intelligence.
Conversely, the end of co-party status is, in principle, the point in time at which a co-party ceases to meet the legal criteria set out above. This can, but need not, involve a complete cessation of activities supporting the other co-parties. It would suffice if a (hitherto) co-party changes its actions such that they no longer meet the two criteria for co-party status. For example, if a state that has conducted airstrikes as part of a coalition alongside its partners, then moves to merely delivering combat aircraft to those partners, it would no longer be a co-party. The same would be true of a state that has previously provided targeting intelligence which reduces its activities to reconnaissance or surveillance operations. In practice, however, it is useful to require evidence of a relevant change of pattern of that co-party’s actions over a prolonged period – i.e. the co-parties’ actions must have fallen below the legal criteria for co-party status ‘with a degree of stability and permanence’ to avoid the legal uncertainty of ‘revolving door’ situations.
Some legal effects of (co-)party status extend after the end of that status. For example, parties must still discharge certain obligations flowing from their party status after they cease being a party, such as obligations under IHL regarding persons deprived of their liberty.
2.4 ‘Proxy wars’
Military assistance in war, whether provided by states or armed groups, frequently generates claims that the conflict has become a ‘proxy war’, implying that it is actually fought by those providing the assistance. Such claims are often political in nature, and it is not always possible to make sense of them in legal terms. They do, however, raise the question of whether and at what point control over a party to an armed conflict makes the state (or non-state entity) exercising that control itself a (co-)party to the conflict.
‘Control over a party’ is not a separate legal test for becoming a co-party that would somehow coexist or even conflict with the framework outlined above. If a state controls another state or armed group to the point that the action of the ‘proxy’ can be attributed under international law to the controlling state, only that controlling state is considered a party to the conflict. This is because, under international law, the proxy does not then act in its own right. There is no room for co-party status if there is only one subject that acts as a matter of international law.
‘Control’ can mean many different things. Where the alleged ‘control’ is below the threshold of attributing it to the controlling entity, there is still room for co-party status. In such cases, however, whether the entity exercising such ‘control’ is a co-party alongside the controlled entity can and should be assessed simply by reference to the criteria outlined earlier in this section. There is no need for any additional or separate criteria.