State Responsibility for Assistance to Foreign Forces (aka How to Assess US-UK Support for Saudi Ops in Yemen)

Airstrikes in Yemen by the Saudi-led coalition have received increased attention in the last few weeks. In her recent post, Beth Van Schaack noted that in addition to the potential responsibility of Saudi Arabia and its coalition partners, international law may also inculpate other States that are providing assistance to the Saudi-led coalition. Such responsibility is founded on the rule reflected in Article 16 of the International Law Commission’s (ILC) Articles on State Responsibility.

In this post, we focus on the rule in Article 16. Before setting out its elements, three clarifications are necessary. First, we are not concerned with individual criminal responsibility under international law, either of the agents of the coalition forces or of the agents of the assisting states (cf. Ryan Goodman’s forthcoming post on aiding and abetting war crimes). Our concern is with state responsibility solely. Second, Article 16 is not the only potentially relevant rule of international law. We do not consider, for instance, the obligations on States imposed by the Law of Armed Conflict, the Arms Trade Treaty, or Article 41 of the Articles on State Responsibility. Finally, we do not make any judgement on the alleged actions by the Saudi-led coalition (see Alex Whiting’s post) or on any specific instance of an assisting State’s responsibility. This post is confined to the generally applicable legal framework for States that provide support to another State’s military operations.

The Rule in Article 16

Although its inclusion in the Articles on State Responsibility was once considered by the ILC to be a matter of progressive development of the law, Article 16 was declared by the International Court of Justice in the Bosnian Genocide case to reflect customary international law (para. 420). A State is responsible under Article 16 if four conditions are met:

  1. The State aids or assists another State in the commission of an internationally wrongful act;
  2. Such aid or assistance contributes to the commission of that act;
  3. The assisting State has intention to facilitate and/or knowledge of the circumstances of the internationally wrongful act; and
  4. The recipient State’s act would also be wrongful if committed by the assisting State.

Of course, to set out the elements so neatly disguises numerous complexities in the legal standard and in its potential application. For present purposes, the first and fourth elements raise few difficulties. In respect of the first, it is clear that any method of support is caught by the rule – the transfer of weapons, the provision of technical support, the sharing of intelligence, and so on. In respect of the fourth, we will assume that the wrongs of the recipient States are breaches of customary international law – barring an exceptional situation such conduct would also be wrongful if committed by the assisting state.

That leaves the second and third elements – the nexus between the assistance and the principal wrong and the knowledge or intentions of the assisting state. On the second, there is disagreement. Some scholars argue that the Commentary requires that the assistance contribute significantly to the principal wrong. The Commentary, however, states only that a significant contribution is “sufficient,” not that it is necessary. When the Commentary turns to the degree to which an assisting State may be held responsible for its acts, the ILC contemplates situations in which “the assistance may have been only an incidental factor in the commission of the primary act, and may have contributed only to a minor degree, if at all, to the injury suffered.” We assess that the latter threshold is likely too low as a matter of customary international law. Nevertheless, in the present context, assistance in the form of weaponry that contributes to specific strikes will likely meet the much higher threshold (a “significant contribution”).

The third condition – the fault required of the assisting State – is the most disputed element of the rule. Here, responsibility lies partially with the ILC itself, as the standard is formulated in three different ways. The plain text of Article 16 refers to “knowledge of the circumstances of the internationally wrongful act;” then paragraph 1 of the ILC’s Commentary refers to assistance provided “with a view to facilitating” an internationally wrongful act; and then paragraph 5 of the Commentary specifies that no responsibility arises unless the assisting state “intended … to facilitate the occurrence of the wrongful conduct.”

That the fault element for what is essentially an inter-State complicity rule is the subject of dispute should be no surprise; domestic criminal complicity has long grappled with this issue. During the long drafting process of the Articles on State Responsibility, States expressed a range of views – the 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.

Contextualizing the Elements

Two other points are worth noting. First, the underlying factual situations at issue are dynamic, and government decision-making must often rely on imperfect information. The critical point is that a potential assisting State’s fault may shift over time. It may be that an initial decision to provide support was made in the absence of the requisite fault. Thereafter, as more information becomes available the assisting State may be required to reconsider its decision to continue its provision of assistance. Continuing to provide support once it becomes clear that such assistance is significantly contributing to the ongoing commission of internationally wrongful acts would be widely understood to render the assisting State responsible.

Second, there are steps that a potential assisting State can take to mitigate the risk of the principal wrong being committed and, in doing so, mitigate its risk of responsibility under the rule in Article 16. In the context of arms exports, for instance, many States already take a range of mitigating measures. More broadly, training, monitoring, and capacity building are possible. Moreover, States can choose to directly support particular units or entities within the recipient State. At least in some cases, this may be a feasible option.

In many cases the legally available options for an assisting State, as a matter of international law, will be to find effective mitigation measures or else to desist. 

About the Author(s)

Ryan Goodman

Co-Editor-in-Chief of Just Security, Anne and Joel Ehrenkranz Professor of Law at New York University School of Law, former Special Counsel to the General Counsel of the Department of Defense (2015-2016). You can follow him on Twitter @rgoodlaw.

Miles Jackson

Departmental Lecturer in Law at the University of Oxford, Author of "Complicity in International Law" Follow him on Twitter (@milesmjackson).