Much attention has been given in the past to the onset of war—to what causes it. The authors of this timely study argue that what war causes is just as important a question. In The Diffusion of War Randolph M. Siverson and Harvey Starr investigate the “contagion” of war — or how and under what circumstances conflicts grow once they begin.Given the great consequences of the expansion of war—economic costs, human costs, and political change, for the participants and also for the international system—it is essential to ask why some wars spread and why others do not; what states are most likely to join wars and how quickly? Viewing war as a process of conflict escalation, the authors explore these important questions through considerations of opportunity and willingness. They consider how the choice to enter war relates to the geopolitical context in which that choice must be made — demonstrating that in the war experiences of states from 1816 to 1965, the effects of geographical proximity (opportunity) and the political pressures of interstate alliances (willingness) have combined to influence the infectious diffusion of war. This distinctive approach permits a synthesis of previous theory and research on war across academic disciplines and of micro- and macrolevels of analysis. Siverson and Starr offer a valuable perspective on the changing nature and process of war; their book makes broadly accessible a subject of vital relevance to the world community.

Randolph M. Siverson is Professor of Political Science, University of California at Davis.Harvey Starr is the Dag Hammarskjöld Professor in International Affairs, University of South Carolina.