Many realist international relations theorists characterize realism as a perspective grounded in a firm grasp of the tragic constancy of human nature and the autonomous role that power plays in human politics. Realism is thus cast in opposition to the hopeful, but often nave, optimism of liberals who seek to steer international relations theory and ethics away from these historical realities. This paper examines the philosophical roots of theories developed by four realist thinkers, Max Weber, E.H. Carr, Hans J. Morgenthau, and Henry Kissinger, in postmodern epistemology and ethics, perspectives not often associated with constancy or notions of objective historical truths. I argue that the origin of their respective theories in Nietzschean epistemology plays a profound role in undermining their ability to develop a credible view of international ethics. Though each of them is, in his way, committed to democratic principles, their works assert an existential, private morality that is incompatible with the ethical requirements of a modern, democratic society.