Revision with unchanged content. Democratic peace theory tends to view democracy in homogeneous terms. There are theoretically compelling reasons, however, to believe that variations in democratic institutions and leadership can influence foreign policy outputs. As executive leadership is most often the center of foreign policy decision-making, one may logically question the degree to which institutions constrain leaders. This study investigates how variations in both leadership and institutions can affect whether democracies pursue conflictual or cooperative foreign policies. The findings here indicate that leadership, institutions, and the interaction between these two variables, what I call the leadership/institutions nexus, play a significant role in shaping the international behaviors of democracies. This suggests that democratic peace theory would be better served by interpreting democracy in a more heterogeneous fashion. The book is designed to assist academics and foreign policy practitioners as well as avid followers of international relations.