Earth's billions of people reside in nearly two hundred countries characterized by varying levels of development, governed by numerous forms of political organization, and adhering to the traditions of widely disparate cultures. Could it possibly be that these obviously different peoples conform to common patterns in when, how and whythey go to war against others? One might be tempted to immediately answer “no” or at least “doubtful.” But others might answer “of course,” perhaps citing similarities such as taboos against incest that are common in virtually every culture and society. In this book I ask whether general knowledge about when wars are likely to occur is possible. In an attempt to understand war onset generally, I consider patterns of war and peace among the great powers, as well as in four minor power regions of the globe.

The research project culminating in this book began as a relatively straightforward effort to determine whether a well-established theory of great power interactions could be modified to help understand interactions among minor powers. The theory modified is power transition theory, which posits a hierarchical international system and emphasizes the importance of relative power relationships and the incentives and disincentives states face in their considerations of acting to change the formal and informal rules that govern their interactions. In order to extend the theory to minor powers, careful consideration must be paid to identifying the international sub-systems within which such states interact. This leads to a new operational definition of regional sub-systems.