War was a defining feature of the twentieth century. A vast percentage of the people of the last century were participants or victims in one way or another of the endless stream of civil and interstate wars that characterized this era. These wars and their consequences were accompanied by unprecedented levels of ethnic cleansing and genocide. I am just old enough to remember World War II, which had a profound impact on my choice of career, discipline and research agenda. I have authored numerous books and articles on various aspects of conflict management and resolution. I have written about intelligence failures and bad crisis management responsible for wars. More recently, in A Cultural Theory of International Relations, I use the origins and dynamics of ancient and modern wars to elaborate and evaluate a broader set of arguments about systematic variation in the propensity and character of cooperation, conflict and risk-taking. In this book, I turn to war itself, with the goal of analyzing its causes in the past and the likelihood that they will diminish as motives for war in the future.

In 2009, when I wrote Why Nations Fight, I was James O. Freedman Presidential Professor of Government at Dartmouth College and Centennial Professor of International Relations at the London School of Economics and Political Science. I want to thank colleagues at both institutions with whom I discussed the premise and arguments of the book and from whom I received useful feedback on the manuscript.