A veteran historian looks back on the great ideological battles of the twentieth century. His familiar but engrossing thesis argues that both communism and fascism stemmed from the dangerous spread of "rogue ideologies" that harnessed military power and totalitarianism for the advancement of utopian ideas. Chapters on Nazism and Soviet communism explore how ideology's romantic appeal in Russia and Germany after World War I extinguished independent political thought and empowered the state. In Conquest's view, Western societies responded weakly to this challenge because intellectuals succumbed to its grand visions and politicians misjudged its potency. Conquest then tries to go further and apply these lessons to the present. He warns that dangers still lurk, even though we may live in a less ideological era. But he does not discuss how ideology applies to other major social forces, such as capitalism and nationalism, and leaves it unclear to the reader how to assess its danger. Nor does he explain how his final warning -- that the idea of "Europe" will threaten democratic rule and divide the West -- relates to the ideological battles of the past.