Like most historians, many students of international politics have been skeptical about the possibility of creating a theory that might help one to understand and explain the international events that interest us. Thus Morgenthau, foremost among traditional realists, was fond of repeating Blaise Pascal's remark that “the history of the world would have been different had Cleopatra's nose been a bit shorter” and then asking “How do you systemize that?” His appreciation of the role of the accidental and the occurrence of the unexpected in politics dampened his theoretical ambition.

The response of neorealists is that, although difficulties abound, some of the obstacles that seem most daunting lie in misapprehensions about theory. Theory obviously cannot explain the accidental or account for unexpected events; it deals in regularities and repetitions and is possible only if these can be identified. A further difficulty is found in the failure of realists to conceive of international politics as a distinct domain about which theories can be fashioned. Morgenthau, for example, insisted on “the autonomy of politics,” but he failed to apply the concept to international politics. A theory is a depiction of the organization of a domain and of the connections among its parts. A theory indicates that some factors are more important than others and specifies relations among them. In reality, everything is related to everything else, and one domain cannot be separated from others.