The world has turned round many times since Harry S. Truman permitted the U.S. Army Air Forces to drop atomic bombs on Japan. Having borne the full moral responsibility for opening the age of nuclear warfare, he courageously repudiated advisers who would have him repeat the macabre performance in Korea or China. His five-star successor, Dwight D. Eisenhower, constructed a magnificent nuclear armory and resolutely refused to use a single weapon in the inventory, despite the proclivity of his secretary of state for saber-rattling warnings of imminent Armageddon. After the bone-chilling scare of John F. Kennedy's Cuban missile crisis, a long period of mature Soviet-American nuclear diplomacy and restraint settled over Washington and Moscow. The well-understood rules of the nuclear-diplomatic road did not become obsolescent until the dissolution of the Soviet Union in 1991. Thereafter, the restless new nuclear powers and a freshly assertive China cast the most ominous shadows over the future. It would take extraordinary American statesmanship to steer a safe course through a world of revanchist states armed with weapons of mass destruction. George H. W. Bush, William Jefferson Clinton, and George W. Bush were only the first of a long line of American presidents who would face a challenge for which the Cold War's nuclear policy offered precious little direct guidance.