To Intervene or Not to Intervene

Abstract

Alliances are related to the occurrence of conflict. A theoretical model predicts how alliance reliability affects the occurrence of conflict in the international system. Suppose that two nations are at war. The intervention of a third nation into this war affects the likely outcome. Nations prefer to fight wars that they expect to win. Nations are more likely to involve themselves in wars in which they anticipate allied support. Estimates of alliance reliability are obtained and used to demonstrate that nations consider alliance reliability when deciding whether to become involved in conflict. For example, nations with unreliable allies are more likely to surrender if attacked than are nations with reliable allies. Alliance reliability affects the occurrence of war. Unfortunately, whether an alliance is honored is only observable when a war actually occurs. The author discusses the sampling bias that this creates.