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Right from the start, the nuclear age was wrapped in a paradox. An awful weapon had saved lives; a terrible instrument of war had brought peace. The images from Hiroshima seared the consciousness of a generation, forever serving as an admonishing reminder of mankind's destructive capacities. "In an instant, without warning, the present had become the unthinkable future," TIME wrote one week after the dropping of the bomb. And yet the very memory of the bombings of Hiroshima and Nagasaki, of cities being reduced to rubble in an instant, provided an odd hope that such terror would never be allowed to happen again. After Hiroshima, the U.S. and the Soviet Union built thousands of nuclear devices, and the threat of nuclear war kept a political and ideological contest within bounds. Buried in silos in the wheat fields of North Dakota, tucked into the torpedo tubes of Soviet submarines parked in the North Atlantic, slung in the bomb bays of B-52s, the American and Soviet nuclear arsenals mutually assured the destruction of both sides if hostilities commenced. The cold war turned into a long peace.
But press that logic further, and you arrive at an uncomfortable place. If nuclear weapons are so great at keeping the peace, why shouldn't everyone have them? And what happens when the Bomb falls into the hands of those who don't remember the legacy of Aug. 6--or simply choose not to? Sixty years after Hiroshima, 14 years after the Soviet Union imploded, the great question facing strategists--facing all of us--is less how a nation might array its nuclear forces and more how to stop the proliferation of nuclear weapons from spinning out of control. The Bush Administration has publicly declared that it is intolerable for states such as North Korea and Iran to get nuclear weapons, but few experts believe that either regime would risk annihilation by actually launching a nuke in anger. More terrifying is the possibility that malefactors operating without such restraints--such as the suicidal jihadists of al-Qaeda--might acquire atomic materials. It is the global terrorist threat that has made this the least predictable moment since the dawn of the nuclear age. Says Sam Nunn, the Democratic ex-Senator: "The terrorist threat is, to me, the most likely use of a nuclear weapon."
To be sure, the challenge of proliferation has been with us from the start. On Aug. 5, 1945, the day before Hiroshima, the possibility of nuclear weapons was hardly a secret. (At least two crew members of the Enola Gay guessed the nature of their cargo before Tibbets told them on the flight from Tinian.) The key theoretical and laboratory work on nuclear fission had been done and published by 1939, and since the community of physicists included Americans, Britons, Germans, French, Italians, Swedes, Russians, Hungarians and Japanese, no one country ever had a monopoly of nuclear know-how.