This introduction presents an overview of the key concepts discussed in the sub sequent chapters of this book. It explores the moral complexity of statecraft in the context of decision-making on armed intervention in the post-Cold War era. The book also adds the debate on humanitarian intervention by analyzing the moral complexity of state leadership when confronted with situations of severe human rights violations. By examining the moral complexity of state leadership, it suggests that in order to gain a clearer understanding of the concept of moral responsibility in international relations, the moral stance of states and policy-makers must be separated from the moral stance of individuals. The book argues that an international community serious about the pledge of never again must address this complexity in order to avoid continued inconsistencies in response to mass atrocities. As the strongest member of the Security Council in the Cold War-era, the United States has been essential to any large-scale humanitarian initiative.