International relations theories can be examined through different paradigms. Realism focuses on self-interest and balance of power, and is divided into classical and neo-realism. Classical realist Hans Morgenthau believed national interest was based on balance of power, military force, and self-interest. Realism analyzes power on four levels, distinguishing power from influence and examining the distribution of capabilities in the international system. Liberalism emphasizes cooperation and interdependence between states and the role of international institutions and law. Constructivism views identities and norms as socially constructed rather than fixed.