By contrast with liberal-cosmopolitan ethics, this book argues that the right analytical starting point for thinking about war and political violence is the use of lethal force to defend against enslavement, not the defence of lives against attempted murder. Enslavement highlights the importance of dominating power as a facet of all violent threats and illuminates more fully than other types of threat the intimate relationships between violence, vulnerability, and social domination. Building a republican account of war ethics around this insight helps identify distinctively political dimensions of violence that are otherwise apt to be overlooked. It provides a compelling basis for understanding the legitimacy of armed defence against a wide range of threats, some lethal, some not.