Debates about humanitarian intervention endure because they pose some of the most important political, legal, and moral questions of our time: about the meaning of sovereignty, the nature of international law, the just use of force, and the nature of international order. Humanitarian intervention in practice remains highly contentious because of the irreconcilable tension between the hope of achieving liberal internationalist aims using the ultimate realist means, military force. The book begins by looking at the most contemporary conundrum in the debate about humanitarian war: the concept of the "responsibility to protect" civilians in other countries from grave human rights abuses, even by resort to force, and traces the debate at three levels. First, it shows how decision makers grappled with three main aspects of decisions to use force: authorization, justification, and obligation. Second, the unique contexts of four NATO nations-- Britain, France, Germany, and the United States-- are examined in light of how they influenced national decisions about war. Third, the analysis traces three distinct currents of thought, or worldviews, regarding intervention.