The principle of a “responsibility to protect” civilians from genocide and other crimes against humanity was first endorsed by the UN in 2005 and was used to authorize NATO’s intervention in Libya in 2011. The concept is widely seen as a radical break with older Westphalian norms of sovereignty. But Glanville shows that the idea that sovereign states should enjoy the absolute right of autonomous self-government and nonintervention was not present at the creation of the Westphalian system, in the seventeenth century. He chronicles how, as absolutist rule gave way to liberal democracy and the nation-state spread to regions outside the West, profound shifts took place in the concept of sovereignty; only in the twentieth century did the idea of unconditional rights to self-government and nonintervention solidify, mostly owing to the efforts of non-European peoples who had suffered at the hands of Western colonialism. Ironically, those efforts were a backlash against the irresponsible ways in which European states had long used and abused the loopholes in their own doctrines of sovereignty to justify exploitative interventions. That history ought to weigh on the minds of today’s powerful states whenever they consider how to act on ideas of responsible sovereignty.