The Probability of War, 1816–1992

What factors increase the probability that a pair of states might go to war is the focus of this study. Six hypotheses, derived from the steps to war explanation, are tested by comparing pairs of states that go to war with each other at least once in their history (from 1816 to 1992) with those that do not. It is found that as two states take the various steps to war that have been posited, the higher their probability of going to war. States whose relations are dominated by territorial disputes have a higher probability of having had a war if both sides have had outside allies, have had recurring territorial disputes, have been engaged in an enduring rivalry, and have had an arms race. As each of these factors becomes present, the probability of war progressively increases. Pairs of states whose relations are dominated by nonterritorial disputes also have their probability of war increased if these factors are present, but at a lower level. Of the various factors that increase the probability of war, outside politically relevant alliances seem to have the weakest impact.