International relations (IR) theory is difficult to define. It is often taught as a theory that seeks both to explain past state behavior and to predict future state behavior. However, even that definition is contested by many theorists. Traditional IR theories can generally be categorized by their focus either on humans, states, or on the state system as the primary source of conflict.
Critical IR theory and Feminist IR theory are often considered part of constructivism; however, there is much debate over whether they constitute their own branches
Realism, Liberalism, and Constructivism as the three major branches of IR theory.