An international political theory considers two issues ignored by traditional philosophies of politics. It confronts the problem of the legitimacy of man’s division into separate, sovereign states, and it examines the justification for the belief that obligations to the state are more fundamental than obligations to any wider society of men. These issues receive their earliest and most detailed consideration in Pufendorf’s writings,1 an interpretation of which is salient to the development of contemporary international theory in three respects. Firstly, it indicates the way in which the classic theory of the modern states-system made explicit one of the central tensions of Western culture; secondly, it reveals the failure of that account to resolve the opposition between two concepts of obligation; and thirdly it highlights the difficulties which contemporary international relations theorists face in their attempt to construct a modern theory of politics. Pufendorf’s system can best be examined by distinguishing three parts: its description of the state of nature and the natural law which binds all individuals within it; its attempted justification of the sovereign state, of a civil society which unites only one part of humanity subject to a common moral framework; and its analysis of the types of behaviour which are appropriate within a system of states.