At War: When Do States Supporting Ukraine or Russia become Parties to the Conflict and What Would that Mean? 

In the face of Russia’s aggression against Ukraine, Western States have been scaling up their assistance to Ukraine. In addition to massive economic and financial sanctions against Russia, many States have been delivering weapons and other military equipment to Ukraine. Some States have also been sharing ‘battlefield’ intelligence with Ukraine. The US, for example, has set up a specific portal that enables Ukraine to access in real-time intelligence uploaded by US officials, including about the movements and positions of Russian forces and relevant intercepted communications. There are also reports of US Cyber Command’s ‘cybermission teams’ based in Eastern Europe supporting Ukraine’s operations by disrupting Russian cyber operations and communication channels. Ukraine has desperately called for more extensive military support, including by way of Western States establishing a no-fly zone over Ukrainian territory. Yet, NATO member States have repeatedly made it clear that they do not wish to become parties to the international armed conflict and avoid even just being perceived as such by Russia. This concern has already been raised with respect to the existing support to Ukraine, by, amongst others, government lawyers in the US (see, eg, here, here, and here) and politicians and commentators in Germany (see, eg, here, here, and here).

Reacting to proposals for further Western support to Ukraine, Russia is also attempting to draw red lines. Russia has warned, for example, that it will consider States imposing a no-fly zone or allowing airbases on their territory to be used by Ukraine as participating in the conflict.

At the same time, the question also arises on the other side of the conflict. Russia has launched significant parts of its invasion of Ukraine from Belarus, apparently with the consent of President Lukashenko. This has drawn widespread condemnation from many States as constituting complicity in Russia’s aggression (as recently analysed on this blog). While Belarus continues to deny that it has been participating in the war, Ukrainian officials reportedly warned of an imminent invasion of Belarusian forces alongside Russia.

Against this background of the various concerns and allegations regarding the party status of States providing support to either party in Ukraine, this post, first, briefly explains what it would mean to be a party to an international armed conflict, and, secondly, analyses which legal criteria must be fulfilled to establish that States become parties to an international armed conflict and how these criteria play out in the support scenarios with respect to Ukraine.

What does becoming a party to the international armed conflict mean?

At the outset, it should be recalled that whether a State has become a party to an international armed conflict has no bearing on the lawfulness of the use of force by or against the respective States. That question is governed solely by the jus ad bellum. Western States’ becoming party to the conflict alongside Ukraine would not entitle Russia to use force against them, since, even once States are parties to an armed conflict, every instance of use of force by and against them must be assessed against the prohibition of the use force. As others have shown, other States can lawfully assist Ukraine in collective self-defence against Russia’s armed attack (so long as they act in accordance with necessity and proportionality) and Russia has no claim to self-defence against this self-defence.

Moreover, the prohibition of the use of force also circumscribes and supersedes any potential ‘belligerent rights’ that would have traditionally flowed from being a party to a war, such as establishing blockades or seizing contraband, or using force in reaction to potential breaches of neutrality law (see here and here). Whatever the current relevance of ‘belligerent rights’ (see Andrew Clapham’s critical assessment here and here), they cannot grant any State permission to use force beyond the confines of the jus ad bellum.

Nonetheless, identifying whether a State is a party to an armed conflict is crucial because the  regulation of armed conflicts by international law is, in many respects, organised by reference to whether the addressee of particular rules are parties to the conflict or connected to such parties. The parties bear central sets of obligations under international humanitarian law (IHL), both under the law on means and methods of warfare and under the law relating to the protection of individuals (I explain in greater detail how the obligations of parties play out between multiple parties on the same side of a conflict in a forthcoming article.) At another level, party status also matters for the legal position of individuals in an armed conflict. The nature of the connection of individuals to a party determines which sets of protective rules apply to them in an international armed conflict. This connection may also influence the scope of individual obligations and may feed into establishing international criminal responsibility for certain war crimes that presuppose a specific connection of the individual to a party. ore subtly, that connection may constitute a factor in assessing the nexus requirement for war crimes. Identifying who is a party also matters for applying neutrality law (which governs the relations between parties and third parties) and the obligation of third States under Common Article 1 of the Geneva Conventions and customary international law not to provide aid, assistance, or encouragement to the parties’ IHL violations. In addition to its relevance for determining the personal scope of obligations during armed conflict, identifying which States qualify as parties to an international armed conflict is relevant to determining the geographical scope of IHL’s application.

Finally, a State’s party status can also have implications beyond IHL. For example, being a party to an armed conflict can potentially modify the way in which certain human rights obligations apply, including the right to life and to personal liberty and security (the unsettled and controversial contours of such modifications are beyond the scope of this post). It can also have implications for applying treaties such as the Montreux Convention—recently relied on by Turkey to restrict access to the Turkish straits to warships (see here, here, and here for analyses)—which contains different provisions for ‘wars’ to which Turkey is a party. Besides the international law implications, States’ domestic law may attach relevance to whether a State is a party to an armed conflict (under international law), regarding, for example, constitutional authority to deploy armed forces abroad or criminal law offences such as treason.

Having considered what party status means, we can now turn to what would make States parties to the conflict in Ukraine.

What makes States parties to the international armed conflict?

There have been persistent suggestions that third States would become parties through violations of neutrality obligations, at least if such violations are ‘significant’ or ‘substantial’, and ‘systematic’ (see, eg, here and here). As Michael Schmitt has recently recalled, violations of neutrality law and the termination of neutral status with respect to an international armed conflict are best kept separate (on whether neutrality law applies to the conflict and whether the actual or contemplated support to Ukraine would indeed violate neutral States’ obligations, eg, here, here, here, and here). Apart from the conceptual difficulty of construing an act as violating an obligation from a status that the act itself terminates, the very existence of the traditional enforcement measures under the law of neutrality for violations that a party can take against a neutral State suggests that States retain their neutral status even after violating neutrality law. Moreover, connecting party status to neutrality violations would raise questions about how to deal with prima facie neutrality violations covered by (collective) self-defence or a UN Security Council mandate. State practice too does not seem to have drawn a connection between neutrality violations and party status.

Traditionally, ‘acts of war’ rather than violations of neutrality’ were required for a third State to become a party to a conflict (see here at p 753). The contours of what this would mean have not received much attention. One approach under current international law could be—as Michael Schmitt suggests—to turn to the requirement for the existence of an international armed conflict, i.e., resort to armed force between States. Conceptually, it should still be noted that there is no need, strictly speaking, to require that a State’s conduct meets the requirements that would have sufficed to create a new international armed conflict in order to become a party to a conflict that already exists. In any event, however, it makes sense that the relevant acts must form part of the hostilities or military operations that constitute the international armed conflict. This would be the case if they have a sufficiently direct connection to harm to the adversary. Sir Christopher Greenwood, for example, has suggested that such a connection would qualify support as an ‘act of war’ which makes the assisting State itself a party (see here at p 58). To illustrate, this direct connection to harm was the basis for the US to qualify certain States as its ‘co-belligerents’ against Iraq in 2003 in light of their support to the US. Conversely, the absence of such a connection was the basis for the Netherlands not to consider Kuwait as a party to the conflict between Iran and Iraq in the 1980s, despite Kuwait’s assistance to Iraq. One practical way to assess this connection could be to require directly causing harm in one step or forming an integral part of coordinated military operations that do so (as the ICRC has suggested in the context of direct participation by civilians in hostilities and to establish when a State becomes a party to a pre-existing non-international armed conflict). To be parties to one and the same international armed conflict, the respective States must arguably also closely coordinate their operations. Precisely what degree of coordination is required is unsettled. It would seem to suffice that each co-party has a role in the decision-making processes on the coordinated military operations.

Against this background, using force against Russian aeroplanes to enforce a no-fly zone in cooperation with Ukraine would certainly make Western States parties to the conflict (see here for operational background and a legal assessment). Supplying arms, without more, would not have a sufficiently direct operational connection. By contrast, the provision of intelligence to Ukraine may form part of concrete military operations, such as targeting processes. Much depends on the concrete circumstances, which are naturally not known publicly. The US has vaguely stated that it has ‘been sharing intelligence that includes information the Ukrainians can use to inform and develop their military response to Russia’s invasion’. Nevertheless, US officials have reportedly also stressed that the US has not shared intelligence sufficiently granular ‘explicitly to target and kill Russian soldiers’. For the reported cyber support by the US to Ukraine, the facts necessary for a conclusive assessment are also lacking. It can be noted, however, that if such operations were to be integrated into and closely coordinated with Ukraine’s military operations, they could bear out a sufficiently close connection to harm caused to the adversary to make the State providing them a party.

Where States provide their territory as a launchpad for military operations by one party to the conflict against another party, this could constitute a sufficiently direct connection to harm caused to the adversary through these operations. In the 2003 Iraq conflict, for example, this seems to have been the ground on which the US qualified Kuwait and Qatar—from where the US had launched some of its military operations against Iraq—as its ‘co-belligerents’ against Iraq (but not other States that had permitted their territory to be used for stopovers, such as Ireland, Germany, or Italy). Regarding Russia’s invasion of Ukraine, Belarus can thus arguably be qualified as a party to the conflict alongside Russia—even as reports of an imminent co-invasion of Ukraine by Belarus have not yet materialised—because it has provided its territory for Russian attacks against Ukraine. On Ukraine’s side of the conflict, much would depend on the role that foreign airbases would play in supporting Ukraine’s air operations. From the perspective of making the respective State a party to the conflict, it could make a difference whether Ukraine were allowed to launch air operations against Russia directly from such bases or whether the bases were merely to be used to move aeroplanes to Ukrainian bases to join the conflict at a later stage.

These different scenarios suggest that whether or not other States have ‘boots on the ground’ in Ukraine is not as determinative of their party status as some statements by Western officials have implied it to be.

To be sure, States’ may be immediately concerned less with the concrete legal consequences of becoming a party and more with the political implications of NATO States being ‘at war’ with Russia, a notion that sets alarm bells ringing about a ‘world war’ scenario. The concern not to escalate further a conflict that has already caused unbearable human suffering means avoiding even acting in a way that Russia might perceive as engagement on the adverse side of the conflict. The complex political choice of further courses of actions thus need not and will not necessarily turn on the legal implications of party status. States should, nonetheless, at least bear in mind the legal framework that would govern different kinds of action and thus be aware of whether or not their action renders them a party to the conflict.