International politics is the study of relationships among nations in which each nation-state has its own separate sovereignty and a different set of obligations and duties towards other states. Its study requires the recognition of a thin line between public and private, which is further blurred when dealing with international associations such as cosmopolitan religious groups (the Roman Catholic Church) or ideological ones like world-wide communist movements.
A central topic of international politics is conflict, but it is also a study of the mechanisms of peace-making, and it involves an understanding of power relationships and the interdependence and dependence of states in a world of competing interests. The main form of conflict between states is war, but it can take other forms, including a diplomatic agreement to some degree appeasing an aggressor, as when Neville Chamberlain agreed at Munich with Adolf Hitler; or a collective action in support of an international norm, such as the negotiated reductions of industrial greenhouse gases that are designed to curb global warming.
The field of international politics has developed from the early nineteenth century as a response to a world of increasing international tension and the prospect of large-scale war. Its development has been accompanied by the development of a number of methods to analyse it. These include studies of international law, particularly the League of Nations; various kinds of “devil theories” that attribute the causes of war to munitions makers and capitalists, and imperialists; the realist school stressing the “power drives” of men and states; psychological approaches that emphasize tensions and their role in conflict; game theory and bargaining analysis; and systems theory, with particular emphasis on the interaction of concrete components.