In the study of international relations there exists a number of different theories, which each try to explain the role of the state in world politics. This essay will attempt to critically examine these theories, and give a broad insight into the similarities and differences between them. First the traditional theories of international relations are examined, notably Realism and Liberalism, followed by the more recent theories of IR, such as Marxism, Constructivism and Postmodernism.
             Since the end of World War II, Realism has dominated the field of international relations. As a distinct school of thought Realism places its emphasis on the state as the primary actor in world politics. Realists generally have a pesimistic view of human nature, and a conviction that international relations are necessarily conflictual and that international conflicts are ultimatly resolved by war.
             Realists operate with the core assumption that world politics unfolds in a system of international anarchy, that is a system with no overiding authority, no world government. As a result international relations can be defined as a struggle between power maximising states in an anarchical environment (Morgenthau, 1960: p2). For this reason realism is sometimes refered to as the power politics school of thought.
             The ideas of realism date as far back as Thucydides who's "History of the Poloponneasean War" is recognised as the first attempt to explore conflict in terms of the dynamics of power politics (Evans and Newnham, 1990, p339). However Realism is usually distingiushed between the classical realism of E. H Carr and Hans Morgenthau, and the Neo-Realism of Kenneth Waltz.
             E. H Carr's " The twentieth year's Crisis" (1939) and Hans Morgenthau's " Politics among Nations" (19 ) are the most influential works of classical Realism. This branch of realism is said to be based on three fundamental assumptions: I)...