Realism is the most dominant school of thought in international relations. It views states as unitary, rational actors focused on military power and security above all else. Realists believe human nature is selfish and states are inherently aggressive or obsessed with security. Key realist theorists include Thucydides, Machiavelli, Hobbes, E.H. Carr, and Hans Morgenthau. Realism values maintaining the status quo and is criticized for ignoring non-state actors and other forces like ethics.