Classical Realism is a theory of International Relations established in the post-World War II era that seeks to explain international politics as a result of human nature. The theory is associated with thinkers such as Niccolò Machiavelli and Thomas Hobbes. Modern thinkers associated with classical realism are Carl von Clausewitz, Hans Morgenthau and Reinhold Niebuhr. Classical Realist thought has since been overshadowed by Neorealism after Kenneth Waltz' work became more widely accepted due to the rise of Structuralism in North American International Relations scholarship which favored the latter's emphasis on rationality rather than human nature as cause for political conflict.