The "realist" school of IR theory emphasizes the state as the sole international actor, and one which avoids or enters conflict to serve its particular self-interest. Classical realism holds that material interests and power drive state leaders, whereas neo-realists argue that security (avoidance of conflict) and longer-term interests play a role in preference and decision-making. This school traditionally understands some notion of the inevitability of rivalry and conflict and diminishes the notion that human nature can be overcome through agreements or institutions.
More information