  The realist response came most prominently from Kenneth N. Waltz, who reformulated realism in international relations in a new and distinctive way. In his book Theory of International Politics, first published in 1979, he responded to the liberal challenge and attempted to cure the defects of the classical realism of Hans Morgenthau with his more scientific approach, which has became known as structural realism or neorealism. Whereas Morgenthau rooted his theory in the struggle for power, which he related to human nature, Waltz made an effort to avoid any philosophical discussion of human nature, and set out instead to build a theory of international politics analogous to microeconomics. He argues that states in the international system are like firms in a domestic economy and have the same fundamental interest: to survive. “Internationally, the environment of states’ actions, or the structure of their system, is set by the fact that some states prefer survival over other ends obtainable in the short run and act with relative efficiency to achieve that end” (93).