One of the most striking features of world politics in the last 200 years was the rise of humanitarianism, the sustained efforts by outsiders to save lives and help those too weak to help themselves. Barnett paints an expansive portrait of that ascent, breaking it down into three distinct ages. From the nineteenth century to World War II, humanitarian intervention existed as part of colonialism, commerce, and Western “civilizing” missions. During the Cold War, it became part of the East-West struggle and the worldwide movement toward state sovereignty and national development. The end of the Cold War gave birth to an ambitious project of liberal humanitarianism that was tied to globalization and the spread of liberal democracy and human rights. Barnett’s point is that humanitarianism is a “creature of the world it aspires to civilize,” rather than some sort of abstract ideal that unfolds amid the chaos and violence of world politics. In making that argument, he includes rich details about the visionaries, missionaries, transnational activists, UN agencies, and democracies that intervened in such places as Nigeria, Cambodia, and Kosovo. Barnett is a realist in that he sees geopolitics and self-serving motives at every historical turn, but he is also an idealist, taking seriously the “ethic of compassion” that informs people and governments.