This book examines the justifications for, and practice of, war by the US since 1990, and examines four case studies: the Gulf War, Kosovo, Afghanistan and Iraq. The author undertakes an examination of presidential speeches and public documents from this period to determine the focal points on which the respective presidents based their rhetoric for war. The work then examines the practice of war in the light of these justifications to determine whether changes in justifications correlate with changes in practice. In particular, the justificatory discourse finds four key themes that emerge in the presidential discourses, which are tracked across the case studies and point to the fundamental driving force in US motivations for going to war. The four key themes which emerge from the data are: international law or norms; human rights; national interest; and egoist morality (similar too, but wider than, 'exceptionalism'). This analysis shows that 9/11 resulted in a radical shift away from an international law and human rights-focused justificatory discourse, to one which was overwhelmingly dominated by egoist-morality justifications and national interest. This book will be of much interest to students of US foreign policy, humanitarian intervention, Security Studies, and IR theory.