AuthorBlank, Laurie R.

International law includes two legal regimes relating to war and the use of force: the jus ad helium, or the law governing the resort to force, and the law of armed conflict (LOAC), the law governing the conduct of hostilities and the protection of persons during armed conflict. The former prohibits the use of force by one state against another, except by invitation, in self-defense, or with authorization by the United Nations Security Council, in pursuit of the UN's central goal of "sav[ing] succeeding generations from the scourge of war." (1) The latter seeks to minimize suffering in war by protecting persons not participating in hostilities and by restricting the means and methods of warfare. The separate application of these two bodies of law is foundational, ensuring that the lawfulness or unlawfulness of any resort to force does not affect the protections, obligations, and authorities inherent in the law of armed conflict, and that compliance or lack thereof with LOAC does not determine the lawfulness of the resort to force. In effect, the fact that a state is fighting in self-defense does not give it carte blanche to disregard the fundamental parameters of LOAC, whether in the targeting of persons or objects or the treatment of persons detained or interned. Similarly, the fact that a state launched an aggressive war does not result in a loss of LOAC protections for its soldiers and civilians, nor does the fact that a state complies with LOAC cover up for any violations of the jus ad helium. As reinforced at Nuremberg and in countless courts and tribunals since then, this separation is essential to preserve the fundamental principles and goals of both bodies of law. (2)

Although the dangers of conflating jus ad helium and LOAC are well known and thoroughly examined in jurisprudence and academic literature, the interplay between two foundational concepts in the two bodies of law remains unexplored: the meaning of armed attack and the trigger for international armed conflict. These two definitions or concepts are the building blocks on which much of the international law authority regarding the use of force resides. Armed attack is the threshold for the use of force in self-defense and therefore forms an essential component of the jus ad bellum and, in effect, serves as a gatekeeper for the acceptable use of force. The existence of an international armed conflict triggers the application of LOAC, with all of its attendant authorities, obligations, rights, and protections. Both terms are central to understanding the parameters for the use of force in various ways--and yet each has a different meaning, a different pedigree, and potentially consequential effects on the ability of the other term to serve its purpose. Although the broader debate regarding the simultaneous application of jus ad bellum and LOAC and the continuing application of jus ad bellum throughout conflict (3) is outside the scope of this Article, the interplay and different thresholds for armed attack and for international armed conflict raise challenging questions about the coexistence of the two bodies of law, namely the consequences of an international armed conflict triggered by acts or force that lie below the threshold for armed attack or other triggering of jus ad bellum. Can force be used and how should it be judged in such circumstances?

This Article explores the gap between the definition of armed attack and the threshold for international armed conflict to identify such possible consequences of the different definitions for the application of either or both bodies of law and to consider whether efforts to reconcile the different meanings are feasible and, more importantly, desirable or problematic. The first Part briefly presents the definition of armed attack and the threshold for international armed conflict, with a focus on the purpose of the particular thresholds and definitions for the two terms in order to provide a foundation for the main comparisons and discussion in the rest of the Article. Part II examines the gap between the respective meanings of the two concepts and the potential legal consequences. In particular, this Part analyzes two primary, but opposing, interpretive effects of the gap between the meanings of armed attack and international armed conflict: first, the use of force in situations falling below the threshold of armed attack; and second, the possibility that an international armed conflict could exist without the states engaged in such conflict having the authority to use force against the adversary. Each of these possibilities raises a red flag within one body of law but at the same time hews closely to the basic concept or goals of the other, raising the question of whether this gap matters and, if so, whether some reconciliation is appropriate. The third Part addresses this final question, that of reconciliation between the two definitions and examines what such reconciliation might look like. More important, attempts at reconciliation could cause a severely damaging blow to one or the other body of law, such that preserving the gap--that is, agreeing to disagree, in effect--is the better course of action.


    As in any other area of law, in both the jus ad bellum and LOAC, effective implementation of the law rests on definitions that create the framework for the application of the law, including rights, responsibilities, and protections. This Part therefore presents and examines the definitions of armed conflict and international armed conflict to set the stage for the analysis and comparisons to follow. Equally important, this Part explores the purpose behind these definitions so as to provide the requisite tools for exploring whether the gap between the definition of armed attack and the threshold trigger for international armed conflict can or should be reconciled or whether the continued dissonance between these two foundational concepts is the better result.

    1. The Meaning and Purpose of Armed Attack

      Armed attack is a critical threshold for the use of force in the international system. The international legal framework governing the use of force, set forth in the United Nations Charter, is comprehensive. In particular, Article 2(4) of the UN Charter prohibits the "use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations." (4) International law provides three exceptions to this prohibition against the use of force in or against another state: the consent of the territorial state; (5) UN Security Council authorization for the use of force,'' usually through multinational operations; or individual or collective self-defense. The last exception, self-defense, is where the meaning of armed attack is relevant--indeed essential--and the focus of the instant discussion.

      The international law of self-defense provides that states may use force as an act of individual or collective self-defense in response to an armed attack or to forestall an imminent armed attack. Article 51 of the UN Charter states: "Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security." (7) This provision thus recognizes the preexisting right of states to use force, including in response to another state's request for assistance, in self-defense against an armed attack. As a result, "armed attack" is the prerequisite--the trigger--that provides the victim state with the right to use force. Indeed, in the Nicaragua case, the International Court of Justice "proceeded from the assumption that the existence of an armed attack is a conditio sine qua non for the exercise of the right to individual and collective self-defence." (8) Although the question of who can launch an armed attack remains the subject of extensive debate, (9) that question is outside the scope of this Article, which centers on the threshold of armed attack--the amount or intensity of the acts involved, in effect.

      The Charter of the United Nations does not define "armed attack" and "[t]here is no explanation of the phrase 'armed attack' in the records of the San Francisco Conference, perhaps because the words were regarded as sufficiently clear." (10) An armed attack is generally understood to be more severe and significant than a use of force, meaning that an act may constitute a use of force without rising to the level of an armed attack. (11) A key part of defining armed attack, as discussed in greater detail below, is therefore to distinguish the gravest forms of force, i.e., those that constitute an armed attack, from the category of "measures which do not constitute an armed attack but may nevertheless involve a use of force." (12) However, international courts "have never provided sufficient guidance on the level or kind of violence that satisfies that threshold [, but r]ather... have preserved considerable ambiguity on the question of when the armed-attack threshold is met and, therefore, whether Article 51 is triggered." (13)

      As a starting point, the International Court of Justice's (ICJ's) jurisprudence focuses on the "scale and effects" (14) of any particular hostile action directed at a state in order to determine whether it rises to the level of an armed attack. Courts and scholars generally differentiate between low-level uses of force and those that are of sufficient gravity and severity to reach the level of an armed attack. The Nicaragua Court suggests that a "mere frontier incident" does not rise to the level of an armed attack. (1)'' Similarly, the Eritrea-Ethiopia Claims Commission determined that "geographically limited clashes... along a remote...

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