The book’s title proposes a reconciliation between two great rival schools of political theory. As Rutger Bregman notes, people have had visions of a perfect, “utopian” world for centuries, but the 20th century witnessed major attempts to implement practical schemes for changing the world, especially in the field of international politics. The catalyst for these efforts was World War I (1914-1918), which killed millions and traumatized millions more. The horrors of that conflict spurred a campaign to ensure that such destruction never happened again, eventually culminating in the formation of the League of Nations in 1920. The League was intended to abolish war by providing a forum for diplomacy, encouraging trade as an alternative to fighting, and securing homelands for nationalities (with the notable exception of colonized peoples in Asia and Africa) based on the assumption that multinational empires were most prone to aggression. The League had some successes, but its failures proved more conspicuous, especially its inability to check the rise of hyperaggressive regimes in Japan, Italy, and Nazi Germany. When the outbreak of World War II effectively put an end to the League, a group of scholars calling themselves “realists” issued a fundamental challenge to the very idea of radical change.