The Causes of War

Armed conflict is a recurrent and destructive feature of international politics. Because citizens are eager to avoid it and policy makers are keen to anticipate it, war has long been studied by philosophers. Today, war is a central concern of contemporary international-relations scholars. To understand the causes of war, scholars must first define war, then establish a universe of actors or conflicts in which both war and peace are possible. Next, they must collect data on the incidence of war in the entire universe of cases over a particular period of time, a random sample of relevant cases, a number of representative cases, or a set of cases relevant to independent variables in the theories they are testing. Finally, scholars must use this data to construct quantitative and qualitative tests of hypotheses about why actors fight instead of resolving their differences in other ways and, in particular, why actors initiate wars by launching the first attack.