What Is International Law
International law is a social historical legal tradition that emerged and spread over time to deal with matters between and across polities. This statement may appear obvious, but its full implications point to a thorough reconstruction of theoretical accounts of international law. Part I recounts how Bentham inadvertently created an enduring set of theoretical problems for international law. Part II describes international law as a social historical legal tradition, showing its European origins and diffusion with imperialism, and exposing three slants in international law. Part III broadens the lens to sketch the history of interaction between and across polities and how this has been managed. Part IV details contemporary efforts to deal with this interaction through organizations and transnational law and regulation. With this background in place, Part V elaborates a series of theoretical clarifications. First I unravel several confusions that result from construing state law and international law as parallel categories and conflating system with category. Then I explain why international law is a form of law, although not a unified hierarchical system. Contrary to common perceptions, furthermore, I show that state law and international law are not and have never been separate systems. Finally, I clarify the relationship between international law and transnational law and regulation. Aspects of this theoretical reconstruction may initially appear surprising, but they follow from the insight that international law is a social historical tradition.