The essays include expositions, analyses, and critiques of some of the more prominent and enduring explanations of war. Several authors discuss realist theories of war, which focus on the distribution of power and the potential for offensive war. Others examine the prominent hypothesis that the spread of democracy will usher in an era of peace. In light of the apparent increase in nationalism and ethnic conflict, several authors present hypotheses on how nationalism causes war and how such wars can be controlled. Contributors also engage in a vigorous debate on whether international institutions can promote peace. In a section on war and peace in the changing international system, several authors consider whether rising levels of international economic independence and environmental scarcity will influence the likelihood of war.