During the Cold War, credible security assurances and strong political and legal restraints limited the horizontal spread of nuclear weapons. The end of the Cold War weakened or removed significant security assurances, created a power vacuum in numerous regions, and unleashed forces of nationalism and ethnic conflict, thereby setting the stage for severe problems of nuclear proliferation. In this article, I analyze the current psychological impetus toward nuclear proliferation in terms of dual processes. First, powerful pressures having to do with security fears, power, and prestige now propel the quest for nuclear weapons. Second, the collapse of the Soviet Union weakened many of the restraints that had previously limited nuclear proliferation. Together, these processes encourage perceptions that nuclear proliferation is inevitable and that it is necessary to obtain nuclear weapons to protect one's national security. Although many nonproliferation efforts focus on strengthening restraints, the dual-process analysis suggests that these efforts alone cannot halt the spread of nuclear weapons and that failures of restraint will stimulate additional nuclear proliferation.The bipolar world of the Cold War provided relatively high levels of stability and of certainty about who were one's friends and enemies. Each superpower had a large number of countries within its security orbit, and the North Atlantic Treaty Organization and Warsaw Pact alliances provided strong security assurances for nations that lacked nuclear capabilities or powerful conventional forces of their own. In diverse regions, the superpowers cultivated allies and maintained stability through balance of power, avoiding hostilities that could erupt into widespread, even global, war. During the Requests for reprints should be sent to Michael G . Wessells