International relations theory is the study of international relations (IR) from a theoretical perspective. It seeks to explain behaviors and outcomes in international politics. The three most prominent schools of thought are realism, liberalism, and constructivism. Whereas realism and liberalism make broad and specific predictions about international relations, constructivism and rational choice are methodological approaches that focus on certain types of social explanation for phenomena.
International relations, as a discipline, is believed to have emerged after World War I with the establishment of a Chair of International Relations, the Woodrow Wilson Chair held by Alfred Eckhard Zimmern at the University of Wales, Aberystwyth. The modern study of international relations, as a theory, has sometimes been traced to realist works such as E. H. Carr's The Twenty Years' Crisis (1939) and Hans Morgenthau's Politics Among Nations (1948).