This article examines the claim that the Bush strategy of dealing with developing threats “preemptively” marked a total break with American tradition. It turns out that preventive war thinking played a much greater role in shaping u.s. policy than most people realize. During the early Cold War period, this sort of thinking was by no means limited to the lunatic fringe. Could the United States simply sit back and allow first the Soviets and then the Chinese to develop nuclear capabilities of their own? Many people, both inside and outside the government, were worried about what would happen if America did nothing and thought that the possibility of preventive action had to be taken seriously. In the post-Cold War period, the Clinton administration seemed ready to do whatever was necessary to prevent North Korea from going nuclear; it seemed prepared, in fact, to go to war over the issue. Even in the pre-nuclear world, preventive war thinking played a major role in shaping policy: American policy in 1941 was strongly influenced by this kind of thinking.