The purpose of this essay is twofold. First, it proposes to undertake, in introductory form, one of the many tasks a historical sociology of international relations could perform: the comparative study of one of those relations which appear in almost any international system, i.e., international law. Secondly, this essay will try to present the rudimentary outlines of a theory of international law which might be called sociological or functional.

International law is one of the aspects of international politics which reflect most sharply the essential differences between domestic and world affairs. Many traditional distinctions tend to disappear, owing to an “international civil war” which projects what are primarily domestic institutions (such as parliaments and pressure groups) into world politics, and injects world-wide ideological clashes into domestic affairs. International law, like its Siamese twin and enemy, war, remains a crystallization of all that keeps world politics sui generis. If theory is to be primarily concerned with the distinctive features of systems rather than wim the search for regularities, international law becomes a most useful approach to international politics.