The authors address the question of why some militarized interstate disputes evolve into wars, while others do not. They note from previous investigations that the probability of such disputes ending in war is associated with the types of bargaining behavior adopted by disputants. Particularly important are the degrees of escalation and reciprocity that characterize that behavior. This leads them to ask two questions: first, why do statesmen involved in militarized interstate disputes adopt the bargaining behavior they do?; second, what accounts for variations in outcomes for those disputes in which similar patterns of bargaining behavior are observed? Based upon an analysis of 30 militarized interstate disputes, the authors conclude that (1) escalation in interstate bargaining is strongly associated with the nature of the issues in contention and the types of threat of force initially employed in dispute bargaining, that (2) there exists an association between the relative capabilities of disputants and the degree of reciprocity in bargaining exchanges, and that (3) variations in the outcomes of disputes largely can be accounted for in terms of the interests at stake and the diplomacy of the great powers. These findings prove to be consistent with the basic tenets of political realism, and suggest that the behavior of decision makers engaged in militarized interstate disputes is generally rational in that they respond to cost-benefit considerations.