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The increasing prominence in recent years of non-international armed conflicts that extend across state borders has strained the traditional legal categories that we use to regulate state use of force. Simultaneous with this phenomenon has been growing acceptance that human rights law and international humanitarian law should co-exist, with the former informing interpretations of the latter to varying degrees. Scholars continue to debate vigorously the implications of these developments and how these bodies of law should interact. As Kenneth Watkin’s book Fighting at the Legal Boundaries: Controlling the Use of Force in Contemporary Conflict observes, however, commanders have no choice but to navigate these ambiguities and attempt to reconcile these tensions on the operational level as they engage in hostilities.

Watkin’s magisterial book can be seen both as a work of operational law and a major scholarly treatment of the law governing the use of force. It provides detailed accounts of how situations arise on the ground that evade easy classification in terms of our existing conceptual and legal categories. At the same time, it furnishes a valuable framework for analyzing the features of such operations that are relevant in assessing how force should be used in particular scenarios. Finally, Watkin offers a set of principles for both operational law and broader policy decisions to help navigate the complex terrain of modern security challenges.

Watkin argues that the twenty-first century approach to conflict must be “holistic” in nature. On the one hand, it must it must acknowledge “the simultaneous application of humanitarian and human rights law,” and the greater influence of the latter in shaping perceptions of the legitimacy of violence. On the other hand, it must appreciate that “the altered security environment of this century has witnessed a definite move away from looking at conflict itself as being uniquely conventional or unconventional,” as transnational non-state organized armed groups have emerged that do not resemble traditional armed forces.

This review essay describes the main ideas in Watkin’s rich and comprehensive analysis. It then focuses in more detail on two of his suggestions. The first is that state forces should presumptively operate under law enforcement rules until this is insufficient to meet a threat, even in the course of an armed conflict. This reflects the incorporation of human rights principles as a default policy even when more permissive rules on use of force are available. The second suggestion is that certain hostile engagements with non-state forces may appropriately be characterized as armed conflicts of limited duration, governed by international humanitarian law. These two proposals reflect his view that characterization of the nature of hostilities should depend upon facts on the ground, specifically the nature of the means that states must use in order effectively to deal with a threat.

I then discuss whether this approach should lead to assessments of state use of force that rely on contextual analysis of the weight of the interests at stake in a given situation, rather than on classification of hostilities in one of our two traditional main legal categories. While Watkin does not take this step, I analyze the work of others who make a cogent argument that we should. Ultimately, I conclude that our existing imperfect legal framework is preferable to a purely contextual approach, because of the radically different moral universes that animate human rights law and international humanitarian law.

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10 Journal of National Security Law & Policy 171-236.