14 International Law Beth Simmons The study of international law and interna- foreshadowed the current sharp upswing in tional relations has flourished in the past interest in international law. Not only are decade. This should hardly be surprising. scholars increasingly interested in the grow- These two disciplines have closely entwined ing “legalization” of international affairs, historical roots in the traditional study of they are making tremendous strides in theo- interstate relations and diplomacy (Jeffery rizing and documenting the consequences of 2006). The role of international law in inter- international legal norms and agreements for national relations has for a least a century our understanding of international affairs been at the heart of some of the most impor- more generally. This has led to new fields of tant debates in international relations schol- inquiry in international relations that were arship. Something of an intellectual wedge barely apparent two decades ago. was driven between these two disciplines The first section of this essay defines a few when the social sciences and international key terms and provides some historical back- relations in particular took a behavioralist ground on the relationship between interna- turn in the 1940s and 1950s. The normative tional law and international relations. The and doctrinal approach of many legal schol- second section discusses the major theoreti- ars seemed to have little intersection with the cal approaches, from those that highlight increasingly social scientific concerns of material incentives to those that rest on more international relations scholars to explain, ideational foundations. The third section interpret, and increasingly to predict interna- discusses international law development – tional politics. For a brief period coinciding concepts of legalization, judicialization, con- with the apogee of structural realism of the stitutionalization, and global administrative 1970s and 1980s, international law was law. The fourth section reviews theories widely viewed as irrelevant to the study of and empirical studies of compliance with international relations. public international law. The final section The drought of scholarly work linking concludes that theory has become less com- international law with international relations partmentalized by “school” and empirical ended by the mid-1990s. The study of inter- research has become more rigorous over the national regimes in the 1970s and 1980s past decade. 55769-Carlsnaes_14.indd769-Carlsnaes_14.indd 335252 55/3/2012/3/2012 112:57:312:57:31 PPMM INTERNATIONAL LAW 353 BACKGROUND Some scholars and practitioners make refer- ence to “soft law.” In international relations, Scope and Definitions this can have two meanings. One refers to any written international instrument, other International law can be defined as a body of than a treaty, containing principles, norms, principles, customs, and rules recognized as standards, or other statements of expected effectively binding obligations by sovereign behavior. Or, it sometimes is used to refer to states in their mutual relations. “What dis- the more hortatory or promotional provi- tinguishes law from other types of social sions within a legally binding treaty (Shelton ordering is not form, but adherence to 2009: 69). specific rules of legality: generality, prom- International law is found not only in trea- ulgation, non-retroactivity, clarity, non- ties but in the body of custom that has devel- contradiction, not asking the impossible, oped over time among states. Customary constancy, and congruence between rules international law is based on state practice, and official action” (Brunnée and Toope combined with an understanding that such 2010). International law’s distinguishing practice has developed into an obligatory feature – that which sets it apart from an norm (opinio juris). When a stable practice institution, practice, or political agreement – develops among a sufficiently broad number is its acceptance in principle as binding. of states, and when a large number of them Public international law comprises a set of view the practice as legally binding, it binding rules among states. Increasingly we becomes recognized as a binding principle of can find instances in which such rules international law. Ius Cogens norms are con- govern individuals (international criminal sidered the most fundamental principles of law and some aspects of the laws of war, for customary international law, from which example), but only states (or in some cases, derogation is not ever allowed. While no organizations of states) can enter into inter- single authoritative list of such norms exist, national legal agreements, or treaties. This some examples include prohibitions against binding state-to-state quality distinguishes aggressive war and crimes against humanity. international law from the broader concept A similar set of basic norms are sometimes of international institutions, which can termed erga onmes – obligations owed to all. include nonbinding practices and which, Examples include obligations to refrain from many would agree, can also include rules slavery and torture. Legal scholars have also and principles devised by nonstate actors given attention to a growing body of what (see the chapter by Martin and Simmons in they refer to as “interstitial law,” that is, the this volume). implicit rules operating in and around explicit Study and research on international law is normative frameworks (Lowe 2000). While also distinct from that of international an important source of international law in organizations. While intergovernmental many areas, customary and interstitial inter- organizations are usually based on an inter- national law have been the subject of rela- national legal agreement (the various bodies tively little attention in international relations, of the United Nations are obvious exam- perhaps because they can be difficult to ples), they are also actors in their own right, establish empirically and their causal influ- and are often studied as such. Many interna- ence is hard to study rigorously (Goldsmith tional legal agreements give rise to thin or and Posner 2005). Since much of interna- even no international organizational struc- tional custom – from the law of the seas to tures whatsoever. An extradition treaty, for prohibitions against torture to the law of trea- example, creates no international organiza- ties – has now been codified, IR scholars tion whatsoever. The parties to the agree- have largely concentrated on treaty law. This ment decide when and how to carry it out. article will do the same. 55769-Carlsnaes_14.indd769-Carlsnaes_14.indd 335353 55/3/2012/3/2012 112:57:312:57:31 PPMM 354 HANDBOOK OF INTERNATIONAL RELATIONS International law in history the European international law actually became valid as universal law of the world in Some form of international system of rules the geographical sense” (Yasuaki 2000). has governed relations between independent Most international law histories can therefore political entities for centuries if not millen- be considered the history of European tradi- nia. David Bederman argues that there was tions and structures, developed in the wake “a coherent sense among ancient peoples of the crumbing Holy Roman Empire, the from Near East and Mediterranean traditions scourge of repeated wars, and the rise of that state relations should be conducted in trade and maritime transportation (Nussbaum accordance with established norms and 1954; Butler and Maccoby 1928). values” (Bederman 2009: 115). He notes that ancient law among nations was first and fore- most an instrument for order, used to secure not only stable power relations among sover- THEORETICAL APPROACHES eigns but also to bolster their internal legiti- macy. While the prehistory of legal The Early Twentieth Century agreements between organized groups of humans has been lost in the mists of history, International law and international relations as early as 2500 BCE evidence can be found scholars began an intense, self-conscious of third party arbitration awards regarding dialog in the early twentieth century. One arable land among cities, as well as nonag- window into this conversation is the implicit gression pacts (frequently violated) among debate that took place during the interwar the same (Altman 2004). Ancient Sumerians years on the role of international law in concluded “international” agreements regard- reducing violent conflict among nations. In ing dynastic marriage alliances between many ways, of course, this was a subset of rulers, arbitration in city-state conflict man- the more general debate about the role of agement, and the laws of travel and extradi- power, morality, and law that took place tion for runaway slaves, refugees, and among a variety of so-called legal idealists deserting soldiers at the dawn of recorded and realists in the 1920s and 1930s. E.H. history (Altman 2009). Carr was one of the most prominent com- It is not the purpose of this article to mentators for the latter (and, in fact, is the develop a history of the development of likely source for the “idealist” label). The international law. However, many such histo- “idealists” held in common the notion that ries note that international law has roots in progress in international relations post World the rules and principles developed by the War I was indeed possible, and would likely Roman Empire to govern interactions be built upon the pillars of international