With the collapse of communism, Marxist theories largely dropped out of the contemporary debate over international relations. In this important book, Halliday tries to reestablish the centrality of social revolution -- what Marx called the "sixth great power" of Europe -- in shaping the modern international order. He first takes aim at the notion that revolution merely disrupts world politics rather than alters it. Yet the French, Russian, Chinese, and developing-world revolutions all produced social upheavals with global reach. In fact, state ideology and power are fundamentally connected to underlying social struggles that periodically explode in revolution. The Cold War was as much about the clash between the Bolshevik Revolution and the West as it was about the balance of power. The author does not dismiss the importance of states but sees them as entities challenged -- even captured -- by social and political forces. By reclaiming Marxism's focus on the interconnected character of social conflict, Halliday has resurrected a theme that has, ironically, become more relevant since communism's demise.