When Samuel Huntington died late last year, obituary notices and memorial appreciations noted that the former Harvard political scientist was among the most influential thinkers of the late twentieth century. Huntington served as a mentor to a generation of scholars—but unlike them, he also served as an adviser to Washington policymakers. And his most enduring legacy will be the argument known informally as the Huntington thesis: the idea that global conflict stems from the competing cultural identities of seven or eight “civilizations.” This idea gained cachet after the September 11 attacks