Far too many international legal scholars portray international law as a set of rules that seems to bear no resemblance to the world of international relations that most political scientists would recognize. International legal rules appear to exist on a different plane, far removed from the harsh world of state behavior. As a consequence, it is often hard for political scientists to take international lawyers seriously. The law seems to be the Platonic Form that has no relationship to what “really goes on.” Glennon, however, offers a very different picture. His book begins with the assumption that international legal rules are created through the behavior of states. This creation takes place in two primary ways. First, states create international law through the conclusion of formal, written agreements —treaties. Second, they constitute law through practice that comes to be regarded as the law—what is called customary international law. But just as law is created through this process of custom, so too can the law be uncreated or recreated through this process of state practice. And herein lies Glennon's insight.

In exploring international law dealing with the use of force, virtually all international legal scholars begin with Article 2, paragraph 4 of the United Nations Charter. Article 2(4) provides: “All Members [of the United Nations] shall refrain in their international relations from the threat of 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.” To most, this treaty provision constitutes a general prohibition of the use of force. These “legalists,” as Glennon calls them, have thus spent most of the past 50 years seeking to interpret this law in light of state practice and other rules of international law. In their interpretive exercises, however, they have held fast to the core conclusion that Article 2(4) is still good law, that it still reflects the controlling rule. Glennon, however, insists that Article 2(4) must be subjected to the ultimate test of any rule of international law—state practice. If state practice is so at variance with a treaty provision, then that provision can no longer be considered to be the law. In essence, states through their practice have chosen to reject that law.

It is with this understanding of the constitutive process of international legal rules that Glennon then performs an empirical analysis of state practice. Now it should be noted at the outset that “empirical” is not intended to indicate “quantitative.” Rather, it means an exploration of numerous cases where force was used in the international system and an evaluation of how the international community responded to such uses of force. Glennon examines both interstate and intrastate uses of force. His conclusion is that it is no longer clear that the system of law intended to be established by the United Nations Charter regime is, in reality, the law. On the one hand, the Charter exists in writing; it has not been formally altered. States continue to solemnly pronounce it to be the law. Yet, on the other hand, the practice of states—exemplified by the NATO intervention in Yugoslavia during the Kosovo campaign—reveals a very different set of rules of the game. There are, as he terms them, two parallel universes of law—the universe of the Charter and the universe of geopolitical reality.

The author, however, does not end his discussion with this finding. Instead, he goes beyond his conclusion about the state of contemporary international law to suggest a possible future. For Glennon, the hope to build up a new legal paradigm lies not in a “topdown” approach that would be initiated by a formal change in the United Nations Charter or by Security Council action, but rather in a “bottom-up” approach. This bottom-up approach would begin with regional organizations, like NATO. It was through a costbenefit analysis—not through obedience to the Charter—that NATO decided to intervene in Yugoslavia. While the precise calculations are no doubt complex and will ultimately remain unknown, it seems likely that NATO leaders weighed human rights and security concerns against the principle of nonintervention and a variety of potentially negative political consequences. In the end, they decided to act. Glennon implies that this same type of cost-benefit calculation by regional organizations in the future could lead to the development of a new legal paradigm relating to the use of force. As regional organizations make decisions in the future, new rules could emerge that will ultimately construct an approach to intervention that, unlike the Charter regime, will have true support from the international community. Of course, only time will indicate what direction the law will take, but his suggestions seem to offer much more than any effort to pretend that the law of the Charter is alive and well and living in the real world.

In sum, I believe that Limits of Law, Prerogatives of Power is a book that should be read by both international legal scholars and international relations theorists. It is exceptionally well written, thoroughly documented, and provocative. International lawyers may not like Glennon's conclusions about the fate of the Charter framework, but if law is to mean anything, they would wisely head his counsel. Conversely, political scientists will be comforted by his “realism,” but they will also be challenged by his appreciation of the importance of law, even in a world of geopolitics.