Chapter 18 of Earthopolis: A Biography of Our Urban Planet explores cities’ role as creators and creations of totalitarian states on the left and the right and the march toward humanity’s most horrific acts of self-destruction and “urbicide” during World War II. The chapter begins with a section on the promising urban gender, sexual, and racial revolutions of the 1920s that opened up new urban spaces of pleasure and expression for many people who had lived far more circumscribed roles before. Nonetheless, totalitarians found ways to leverage many different urban spaces into power. They rebuilt cities to strengthen their grip, then to arm themselves for a war of annihilation. New facilities devoted to drilling for petroleum, transporting it, and refining it became central to the course of the war. Acts of mass imprisonment, torture, and racial extermination led to the construction of some of world history’s most horrific built spaces. Meanwhile, the aerial bombing of cities and civilian neighborhoods became routine, culminating in fire bombings and the nuclear explosions in Hiroshima and Nagasaki.