The basic assumption of this study has been that the nature of international relations has not changed fundamentally over the millennia. Believing that the past is not merely prologue and that the present does not have a monopoly on the truth, we have drawn on historical experience and the insights of numerous earlier writers. Although the purpose of this study has been to understand international political change, it also has assumed that an underlying continuity characterizes world politics: The history of Thucydides provides insights today as it did when it was written in the fifth century B.C. One must suspect that if somehow Thucydides were placed in our midst, he would (following an appropriate short course in geography, economics, and modern technology) have little trouble in understanding the power struggle of our age.

This assumption of continuity in the affairs of states has been challenged by much recent scholarship in the field of international relations. Contemporary changes in technology, economics, and human consciousness are said to have transformed the very nature of international relations. International actors, foreign- policy goals, and the means to achieve goals are said to have experienced decisive and benign changes; it is said that the nation-state has receded in importance, that welfare goals have displaced security goals as the highest priority of societies, and that force has declined as an effective instrument of foreign policy. One witnesses, in fact, a curious tension between the prevailing mood of public pessimism and current scholarship on international relations.