Two metaphors began to take hold: the state as a "billiard ball" among other billiard balls on the pool table of the international system; and the state as a "black box," whose behavior could be estimated by the study of external
forces without much inquiry into the idiosyncratic contents of the box, such as domestic politics and leader psychology. Realism, with its emphasis on raison d'etat, combined with scientism, with its envy of the natural law explanations of physics and the seeming powerfulness of economic models, provided a denatured perspective of international politics. It is not difficult to see how game theoretic and rational choice analyses could therefore be constructed as the most useful approaches to the study of international relations. It is not coincidental that the development of this "states
systemic project" took place during the Cold War, which could be viewed as the natural crucible for its development. This project emphasized the importance of system-level explanations of state behavior, at the expense of examining more micro-level explanatory levels that focus on how and why individuals act in international relations.