The apparently accelerating arms race between the United States and the Soviet Union and the precarious political conditions existing in many parts of the world have given rise to new anxiety about the possibility of military confrontation between the superpowers. Despite the fateful nature of the risk, we have little knowledge, as Jack S. Levy has pointed out, "of the conditions, processes, and events which might combine to generate such a calamity." No empirically confirmed theory of the causes of war exists, and the hypotheses -- often contradictory -- that have been proposed remain...