Trump vs. International Law: Using Force After Conflict–Is the Jus ad Bellum Relevant or Just an Afterthought?

[Laurie R. Blank is a Clinical Professor of Law, Director of the Center for International and Comparative Law and Director of the International Humanitarian Law Clinic at Emory University School of Law.]

I want to thank Opinio Juris for the invitation to participate in this online symposium and congratulate Dean Harold Hongju Koh on his new book.

In January 2018, then-U.S. Secretary of State Rex Tillerson declared that the United States would keep military forces in Syria even after the end of the conflict with ISIS, in order to: 1) ensure that “ISIS and al-Qaida suffer an enduring defeat, do not present a threat to the homeland, and do not resurface in a new form”; 2) prevent Syria from ever being a “platform or safe haven for terrorists to organize, recruit, finance, train and carry out attacks on American citizens . . . or against our allies”; and 3) diminish “Iranian influence in Syria” and deny Iran’s “dreams of a northern arch”. Earlier this month, the administration confirmed that it will maintain an indefinite presence in Syria for these purposes.

The commonly-accepted determination that the U.S. decision to pull out of Iraq at the end of 2011 created space for ISIS to emerge as a reconstituted version of al Qaeda in Iraq forms the backdrop to this decision. With that in the rearview mirror, the strategic and policy decision to maintain a military presence to prevent a rebirth or reconstitution of one of the most brutal terrorist groups of recent decades appears straightforward. It also is hard to argue with goals of preventing a safe haven for other terrorist groups or violent actors and pushing back against Iran’s attempts to secure a sphere of influence.

But what about international law? Can a state simply stick around after a conflict is over to prevent a new conflict from erupting or to suppress efforts by other actors to take advantage of the vacuum left by the previous conflict? Is the Trump Administration thumbing its nose at the international legal architecture or creating new precedent in which political or moral justifiability — legitimacy — overrides lawfulness or legality in determining what is right or appropriate as a course of action?

If the United States maintains a military presence in Syria after the end of the conflict with ISIS, the only possible basis could be self-defense: Syria has not consented to the U.S. military currently being in or remaining in Syria and the U.N. Security Council has not authorized and is unlikely to authorize a multinational operation in Syria. Can self-defense be a justification for a state to use force to prevent the resurgence of conflict? Or to deny a safe haven to terrorist groups or a strategic position to another state?

The quick and easy answer is no — any use of force in self-defense must be in response to an armed attack and comply with the requirements of necessity and proportionality, whether before conflict or after a conflict. But is that automatically correct? Does a state that just finished fighting with or defeating a non-state armed group in the territory of another state have to wait until that group attacks it again before it can take action to counter the threat? Perhaps the very fact of a previous conflict, the nature of the adversary group, the nature of the post-conflict environment, or the way in which the conflict ended might change the traditional application of the law. And if so, how far does this reach — only to preventing conflict between the same two groups? Or to preventing conflict in the same area? Or perhaps to a broader set of strategic goals?

As I examine in this forthcoming book chapter, the use of force after conflict for any of these purposes puts significant stress on the jus ad bellum and each of the components of the international law of self-defense: use of force, armed attack, necessity and proportionality. In particular, beyond an overarching question of whether the original self-defense authority at the start of the original conflict extends to cover post-conflict activity, the common thread is whether the existence of a previous conflict alters (or should alter) the meaning of any of these core concepts so as to change how we understand the use of force in self-defense.

As a preliminary matter, maintaining a military presence in the territory of another state after the end of a conflict and without its consent meets the threshold for a use of force, as it would in any other circumstances, and thus triggers the jus ad bellum. One could ask whether the fact that a state engaged in military operations in another state’s territory as part of legitimate self-defense operations changes how we understand continued military presence, or other low-level acts, after that self-defense operation has ended. Although the original self-defense authority could be offered as a justification for the post-conflict preventive action — such that a new jus ad bellum analysis would not be necessary — the better argument is that maintaining a military presence in the territory of another state after a conflict is over is a use of force that requires a proper legal justification.

In the absence of consent or Security Council authorization, such legal justification can only come from self-defense, and then requires the trigger of an armed attack and adherence to the requirements of necessity and proportionality. Although it is axiomatic that the right to use force in self-defense depends on the existence of an armed attack or imminent armed attack, the scenario of preventing the recurrence of conflict introduces two questions in that regard.

First, does the original self-defense authority extend such that a new armed attack is not even necessary? The challenge of identifying the end to conflicts with non-state groups, particularly terrorist groups, and the possibility of continued attacks after the end of the conflict, may lead states to argue that the original self-defense authority continues notwithstanding the start and end of a conflict with the same group, or to assert that they enjoy a residual armed conflict authority that extends to cover acts in the aftermath of the conflict that could spark new violence. Such arguments highlight the dangers of the “forever war” that Dean Koh warns about in his new book.

Second, could the definition of armed attack somehow be different when a state uses force to prevent recurrence of conflict? Several factors might lower the threshold for an armed attack, thus triggering the right to use force in self-defense more easily.

First, the nature of the potential attacker: Although state practice in the aftermath of international armed conflict suggests no change from the traditional conception of armed attack when two states are involved, consider how the aftermath of an extraterritorial conflict against a non-state group, particularly a terrorist group, might contribute to driving down the threshold for an armed attack. After the state has suffered an armed attack and used force in self-defense against the non-state group already, leading to the armed conflict to defeat the group or otherwise end the attacks, the fact that it is that same group from a prior conflict that is engaging in certain acts involving violence or anticipated violence could be significant in leading the state to have a quicker or lower response threshold and thus a less stringent definition of armed attack.

Second, the nature of the acts: Acts that normally would not rise to the level of an armed attack might also be more likely to meet that threshold in the aftermath of a previous conflict — in effect, a gravity or severity “boost” from the prior conflict. The increasing reliance on “hybrid warfare”, the blending of multiple and varied means to gain an advantage, destabilize an adversary, or accomplish other strategic goals, highlights the likelihood of heretofore below-the-threshold acts constituting armed attacks because of the gloss added by the previous conflict. Such below-the-threshold attacks could also find purchase in the accumulation of events theory of armed attack, with either less severe or fewer acts being deemed sufficient to constitute an accumulation of events in the aftermath of conflict in comparison to a situation with no prior conflict or risk of resurgence of violence.

Third, the understanding of imminent: The concept of anticipatory self-defense may change to some degree based on the nature of the prior conflict and the actors involved, allowing for the use of force sooner or for less grave acts than might be ordinarily expected or accepted in a situation where a previous conflict did not color the parties’ intentions or analyses or the perspectives of external actors and observers. Finally, the way in which the previous conflict ended and the location of the acts in question could also alter the understanding of the threshold for an armed attack.

Once the armed attack trigger is met, how do necessity and proportionality apply to the use of force to prevent recurrence of conflict, or safe haven for jihadists, or another state gaining a sphere of influence? Necessity and proportionality focus on whether the defensive act is appropriate in relation to the ends sought when acting in self-defense — as a result, any assessment of self-defense must start with the victim state’s aim or objective in using force in response to the armed attack or imminent armed attack. An essential question, therefore, is whether preventing the recurrence of conflict — or the other goals the United States has identified in Syria — is a legitimate aim of acting in self-defense.

Traditionally, self-defense seeks to end or repel attacks; today, the goals of preventing future attacks and defeating the attacking force entirely are also accepted as legitimate aims of self-defense. Preventing recurrence of conflict lies along the more permissive end of that spectrum; the U.S. goals for a continued military presence in Syria appear to be far broader, however, going well beyond any direct connection to the current conflict with ISIS.

The legitimacy of these stated, or presumed, objectives for using force to prevent the recurrence of conflict, and the application of necessity and proportionality, depend on how well they track the fundamental idea that force can be used in self-defense to halt or repel attacks. The breadth of the possible objectives of self-defense in preventing the recurrence of conflict could result in the necessity requirement becoming irrelevant in the face of an ever-expanding justification for the use of force in some manner. To the extent that the use of force seeks to achieve objectives directly related to the adversary in the previous conflict, it could potentially fit within a generous understanding of self-defense, but objectives that stretch beyond the adversary in the previous conflict are harder to shoehorn into any paradigm for the use of force in self-defense.

Proportionality raises equally difficult concerns. Preventing a recurrence of conflict, in a post-conflict environment before any resurgence of violence occurs, offers few metrics or indicators to identify how much force is needed and whether it is successful, because it is also possible that there would have been no violence or recurrence of conflict without the use of force. Where the state seeks to occupy the potential space, both physical and figurative, where the previous adversary or other actors might nurture and engage in violence, the use of force in self-defense is operating one or more steps in advance of the usual conceptual framework. If the state is successful, no plans or other suggestions of attacks or violence would emerge, leaving no way to consider how much force is acceptable and how much goes too far.

The use of force after conflict — whether to prevent resurgence of conflict or for broader strategic goals — has real ramifications for core concepts in the law of self-defense and thus could stretch the jus ad bellum dramatically, perhaps even to the breaking point. It would be wise to consider the long-term consequences for the law alongside any possible short-term strategic gains.