Brooklyn Law Review


Laurie R. Blank


The prohibition on the use of force is the central pillar of the international system of peace and security, and yet contemporary conflicts continue to stretch and pressure this foundational rule. This article examines how international law applies to the use of force in the territory of another state for the purpose of preventing a resurgence of violence after a conflict has ended. In the absence of consent or U.N. Security Council authorization, can self-defense be a justification for a state to use force to prevent the resurgence of conflict? In January 2018, the United States announced an intended policy of maintaining military forces in Syria after the end of the conflict with ISIS, in order to prevent the resurgence of conflict, prevent Syria from being a platform for jihadists, and prevent Iran from extending a sphere of influence in the area. The backdrop to this decision is the well-accepted determination that the United States’ 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. The strategic and policy decision to maintain a military presence so as to prevent a rebirth or reconstitution of one of the most brutal terrorist groups of recent decades appears straightforward. A more complicated question, however, is how to assess the lawfulness of the use of force in the territory of another country in order to prevent the reemergence of violence. This article addresses a series of issues that stem from the broader question of whether a state can use force to prevent the recurrence of conflict, including whether the meaning of armed attack remains constant regardless of whether it is assessed in the absence of conflict or immediately following the end of a conflict, and how necessity and proportionality apply to such uses of force in accordance with the foundational tenets of the international law of self-defense. The first section addresses introductory issues, including a brief explication of the international law of self-defense, the meaning of the term “use of force” in international law, and the ways in which different types of conflicts end and how to define or identify such endings. The second section analyzes the proper trigger for the right of self-defense, an armed attack or imminent armed attack, and explores whether and how the definition of and threshold for an armed attack might differ in post-conflict scenarios. For example, the nature of the enemy may produce different perspectives on whether and when certain acts constitute an armed attack in this phase between the end of a conflict and a potential reemergence of violence, as could the location of the acts, the types of acts, or even the manner in which the conflict ended. Finally, the third section queries how necessity and proportionality, the key criteria for the use of force in self-defense, apply or should apply to this proposed scenario. Understanding the scope and parameters of necessity and proportionality demands an inquiry into the legitimate aims of self-defense, as well as a nuanced look at how necessity and proportionality operate and what these two essential criteria are designed to achieve and safeguard.