This article is the latest in our Fog of Law series that examines the gray zones in international law and conflict that can be exploited by states. The series comes in advance of an expert workshop on the topic at the US Naval War College’s Stockton Center that Just Security is cosponsoring with the Naval War College and the International Committee of the Red Cross. 

Many States now work with foreign military forces to exert power on the modern battlefield. But what legal responsibilities apply to those States providing assistance to foreign partners who engage in serious violations of international law? Examples of where these questions arise include joint military operations in which coalition partners are responsible for detaining suspected fighters, transferring combatants into the custody of a foreign force, sharing intelligence information, supplying arms, refueling aircraft, and allowing the use of an airbase. What triggers legal responsibility when the recipient of one’s assistance engages in wrongful conduct? There is not one international legal rule that regulates this space, but several. Different, and in some cases overlapping, rules define when States and their officials may be held legally responsible for the conduct of partner and proxy forces.

In an effort to develop and fine-tune our understanding of the international legal architecture, I spell out the different rules that might apply to these relationships. I then explore some thorny questions raised by elements of the different, and sometimes overlapping, categories of rules.

A. Pathways to State responsibility/official liability for the conduct of foreign partners and proxy forces

Category 1. State responsibility – attribution for the acts of non-State actors

example: Articles 8 and 11 of the Articles on State Responsibility

Category 2. State responsibility – aid or assistance to foreign partners

example: Article 16 of the Articles on State Responsibility

Category 3. State responsibility – aid or assistance in maintenance of a serious breach of a peremptory norm of international law

example: Article 41 of the Articles on State Responsibility

Category 4. Common Article 1 of the Geneva Conventions – Duty to ensure respect and due diligence

Category 5. Primary rules in substantive legal regimes

examples: non-refoulement in refugee law and other specific rules in human rights, law of armed conflict, anti-terrorism, arms trade, etc.

Category 6. Individual liability for aiding and abetting war crimes

B. Differences between the Pathways–and conundrums they raise

1. Under rules of attribution (Category 1), is there a settled standard under international law? What should it be? Should legal advisers to governments, for example, warn policymakers about the legal risks entailed in both the high-threshold “effective control” test set forth by the International Court of Justice (in Nicaragua) and the lower-threshold “overall test” set forth both by the International Criminal Tribunal for the Former Yugoslavia (in Tadic) and by the International Committee of the Red Cross (in its 2016 Commentaries)?

Is the test for attribution trans-substantive—in other words, does the same rule apply the same way across different substantive domains of international affairs (from use of force, to environmental law, to conduct of hostilities, etc.)?

In particular for our purposes, does it make sense for the attribution rule for determining whether an international armed conflict exists is set a low threshold (overall control) while the attribution rule for LOAC violations during that armed conflict is set at a high threshold (effective control)?

The International Court of Justice appears to have answered that question in the affirmative. At least the Court held out that possibility in its 2007 Opinion in the Bosnian Genocide case:

“Insofar as the ‘overall control’ test is employed to determine whether or not an armed conflict is international, which was the sole question which the Appeals Chamber was called upon to decide, it may well be that the test is applicable and suitable; the Court does not however think it appropriate to take a position on the point in the present case, as there is no need to resolve it for purposes of the present Judgment. On the other hand, the ICTY presented the ‘overall control’ test as equally applicable under the law of State responsibility for the purpose of determining — as the Court is required to do in the present case — when a State is responsible for acts committed by paramilitary units, armed forces which are not among its official organs. In this context, the argument in favour of that test is unpersuasive.”

In sharp opposition, the International Committee of the Red Cross answered the question in the negative:

“In order to classify a situation under humanitarian law when there is a close relationship, if not a relationship of subordination, between a non-State armed group and a third State, the overall control test is appropriate because the notion of overall control better reflects the real relationship between the armed group and the third State, including for the purpose of attribution. It implies that the armed group may be subordinate to the State even if there are no specific instructions given for every act of belligerency. Additionally, recourse to the overall control test enables the assessment of the level of control over the de facto entity or non-State armed group as a whole, and thus allows for the attribution of several actions to the third State. Relying on the effective control test, on the other hand, might require reclassifying the conflict with every operation, which would be unworkable. Furthermore, the test that is used must avoid a situation where some acts are governed by the law of international armed conflict but cannot be attributed to a State.”

Does one even need to go through an attribution analysis to determine the existence of an international armed conflict if training and equipping an organized armed group involves the introduction of force in a dispute between two States?

How far apart are the Tadic overall control test and Nicaragua’s effective control test? The ICTY Appeals Chamber, in describing the overall control test in Tadic, at an important point includes the element of “supervision” as part of the formula. The tribunal referred to “overall control going beyond the mere financing and equipping of such forces and involving also participation in the planning and supervision of military operations.” In other instances the tribunal did not include supervision as an element: “The control required by international law may be deemed to exist when a State (or, in the context of an armed conflict, the Party to the conflict) has a role in organizing, coordinating or planning the military actions of the military group, in addition to financing, training and equipping or providing operational support to that group.” Is supervision of the conduct of the non-state actor a necessary condition for attribution under the overall test, and if so, does including it as an element significantly reduce the gap between the two tests?

Finally, are there situations in which conduct could be attributable under the effective control test but not under the overall control test? Are there situations in which a State is not engaged in “financing, training and equipping” a non-State actor, but still exercises effective control over the group? Consider situations in which the group is self-financed or receives its training and equipment from elsewhere. Depending on how one interprets the judicial opinions in this space, it appears that the actions of the non-State actor might be attributable to the State under the Nicaragua rule, but not under Tadic. (Thanks to Rafe Andrews for the insight in this line of analysis.)

2. What are the potential differences between aid and assistance to foreign partners under Category 2 and aiding and abetting criminal liability (under Category 6), and what do such differences tell us about each set of rules?

One of the most vexing issues in analyzing the principle of State responsibility under Category 2 is whether the rule requires an assisting State to have an intent to facilitate the actions of the recipient State—and what exactly might be meant by “intent.” Let’s assume that the rule requires something close to a shared desire or purpose to commit the wrongful act; then how does that comport with aiding and abetting liability under international criminal law? Under customary international law, officials can be held criminally liable for aiding and abetting an international crime (e.g., a war crime by a foreign State) even if they do not have a desire or purpose to facilitate the criminal act. As Professor Miles Jackson has explained, it would then be surprising if the state responsibility standard were more restrictive than the international criminal law standard. It would mean that government officials could be held criminally liable for acts that their State could not be held legally responsible. Does that outcome indicate how we should interpret the element of intent in Category 2?

In other respects, aiding and abetting liability appears to be narrower than State responsibility for aid and assistance under Category 2. Aiding and abetting liability may require that the relevant support involves a “substantial contribution” to the commission of the crime. According to the International Law Commission’s commentaries to the Articles of State Responsibility, however, a State may violate international law for providing assistance that involves only “an incidental factor” in the commission of the primary act and that contributed “only to a minor degree” to the injury suffered (for further discussion, see  my earlier piece with Vladyslav Lanovoy). That kind of differential would make more sense. The standard for individual criminal liability would be narrower than the standard for state responsibility, and any violations of the former (along this dimension) would be violations of the latter.

Another question is raised by the comparison between Category 2 and Category 6: Are States responsible for aiding and assisting an organized armed group in the commission of an internationally wrongful act? In other words, the issue is whether Category 2 applies, as a matter of customary international law, to support for non-State actors. Does the fact that Category 6 applies unequivocally to aiding and abetting war crimes by an organized armed group affect that analysis? Would it be incongruous for officials to be individually criminally liable for providing assistance to a non-State actor engaged in war crimes (even without those officials’ sharing a desire or purpose to facilitate the crimes) while their State would not to be held responsible for assisting the non-State actor in the commission of war crimes (even with the desire and purpose of facilitating the crimes)?

Finally, if Category 2 applies to a State’s provision of aid and assistance to non-State actors, do all the elements of Article 16 of the Articles of State Responsibility carry over as well? Consider the element of intent. This purpose element may not be the same in the case of State assistance to a non-State actor. According to the Chatham House report, a key justification for including a high threshold for intent under Article 16 is to avoid “a chilling effect on cooperation between states.” That reasoning works because State-to-State cooperation is generally considered a public good in international relations. That justification, however, doesn’t apply so easily to State cooperation with organized armed groups. There is less reason to think that the purpose element exists at all or to the same degree when it comes to State aid and assistance to organized armed groups. At least military advisers engaged in a legal risk analysis would need to be well informed of this possible distinction.

3. Does Article 41 of the Articles of State Responsibility (Category 3) offer a solution to some of these quandaries?

The rule contained in Article 41 may serve as a residual category applicable to those instances in which a partner or proxy force engages in gross or systematic violations of peremptory norms of international law. Although a limitation of Article 41 is that it addresses only conduct after the fact, it includes situations of repeat violations of international law and does not require a showing of intent on the part of the assisting State. As the Chatham House report explains,  “it could be argued that Article 41 more generally implies that states are under a stricter duty not to render aid or assistance where peremptory norms are invoked, and that the importance of peremptory norms warrants that states should be more careful about the ways in which they cooperate with one another.”

This understanding of Article 41 may obviate the need for other interpretations of Article 16. For example, Miles Jackson and I have written that the competing views about whether Article 16 includes an element of intent might not make much of a practical difference in cases in which a recipient is repeatedly engaged in serious international law violations. In those circumstances, either view of Article 16 could produce the same outcome. We wrote:

“[T]he United States, for one, stated its support for some element of intent (the exact contours of its expressed position are not clear). Other States, and perhaps a majority of scholars, support the standard of knowledge derived from the plain text of Article 16. This debate is ongoing. Nonetheless, it is worth noting that the two positions may not be that far apart (as is often shown in domestic law on complicity). Even if intent were required, if the assisting State’s knowledge of the circumstances approaches something close to practical certainty that the principal wrong will occur, it may be possible to make an inference of intent. Professor Vaughan Lowe QC argues that ‘as a matter of general legal principle States must be supposed to intend the foreseeable consequences of their acts.’ If this is right, whatever the assisting State’s overall purposes, if it knows that its assistance is significantly contributing to the commission of the principal wrong it may be legally responsible.”

Greater attention to Article 41, however, may obviate the need for such an analysis of Article 16 when the situation involves gross or systematic war crimes by a partner or proxy force. It could also obviate the need to resolve quandaries about the existence and scope of any intent requirement when it comes to aid and assistance to foreign partners or proxies engaged in such grave abuses.

Image: Iraqi Army recruits train with U.S. Army trainers at a military base on April 12, 2015 in Taji, Iraq. Photo by John Moore/Getty Images