Furthermore, first or second image theories were insufficient because the prescriptions that followed from them required changes in the relations between states, which implies that the problems themselves stemmed from the nature of the international system, his third image. Explanations of patterns of international behavior, such as the recurrence of war, that were based on conceptions of human nature or the nature of states (his first and second images of international politics) were, at best, incomplete, as human nature theories could not explain why war does not always occur, while theories of national difference could not explain why states with different political systems behave similarly in similar circumstances. The father of structural realism, Kenneth Waltz ( 1959), argued that to understand international politics, we must understand the nature of the international system – the political environment within which states interact. To overcome these challenges, neoclassical realists need to consider a few key avenues for future research, such as generating well-specified neoclassical realist theories of foreign policy and devoting more attention to the domestic politics of international cooperation in order to shed the “competition bias” of neoclassical realism. Nevertheless, neoclassical realism faces a host of criticisms, such as the claim that it is comparatively inefficient and that it is impossible to separate international and domestic variables.
Adherents of neoclassical realism insist that their approach represents a significant improvement on existing approaches to international relations and foreign policy, including “Innenpolitik” approaches. Neoclassical realists have identified a number of important limitations to the neorealist model-for example, states do not always perceive systemic stimuli correctly, or the international system does not always present clear signals about threats and opportunities. Taking neorealism as their point of departure, neoclassical realists argue that states respond in large part to the constraints and opportunities of the international system when they conduct their foreign and security policies, but that their responses are shaped by unit-level factors such as state–society relations, the nature of their domestic political regimes, strategic culture, and leader perceptions. Neoclassical realism is an approach to foreign policy analysis that seeks to understand international politics by taking into account the nature of the international system-the political environment within which states interact.