International politics is the study of power struggles in a world with many different interests and cultures. This field draws upon insights from many disciplines, including history, economics, sociology, psychology, geography, and law, in addition to political science. It is concerned with the relationship between domestic and foreign policy, as well as the overlapping of politics among states, non-state actors, and transnational groups.
The most influential of the theories of international relations is realism, which argues that state action in the global arena reflects its unique national characteristics and therefore often does not project a unified set of interests. Realism also asserts that the world environment is anarchic, and that states cannot know what other states will do.
A more moderate approach is liberalism, which assumes that all states act rationally and self-interested, and that they can cooperate in the face of uncertainty. This theory views the international environment as a “game,” and that cooperation can result from the application of game theory to the behavior of states and their interconnections.
Another view is institutionalism, which combines elements of realism and liberalism. This theory posits that international institutions – like the North Atlantic Treaty Organization (NATO) – can be effective, and can achieve defense, economic, and diplomatic goals.
Lastly, there are constructivist theories of international politics, which believe that the world system is socially constructed. They believe that different international systems reflect different normative positions on the human condition and its relation to power.