Nuclear weapons were an integral part of the US arsenal in the Cold War years. Successive administrations relied on the enormously destructive power of these weapons for the defense of the Western Bloc. The US government, maintaining a final voice in employing nuclear weapons in contingency, rejected its allies' request that the weapons not be used from their bases without prior approval. Nuclear power was also utilized, however, to cement ties with its allies by offering bilateral agreements for the peaceful use of this source of energy.<br>While engaged in the nuclear arms race, the US and the USSR shared a common interest in averting war and preventing nuclear proliferation; both nations began nuclear test ban negotiations in the latter half of the 1950s. The PTBT of 1963 and the NPT of 1968 were two treaties that resulted from these negotiations. Throughout the Cold War years, nuclear mutual deterrence between the two superpowers was maintained, and the NPT was largely successful in controlling nuclear proliferation. The US was estimated to have spent $5.5 trillion on nuclear weapons, which represented almost 29% of all military spending in the Cold War period. The US bore the staggering cost of nuclear weapons regardless of their inherent risk so as to insure Pax America.<br>With the end of the Cold War, nuclear deterrence against the USSR lost its military validity while the accelerating spread of nuclear weapons became a matter of serious concern. Iraq was reported to have reached an advanced stage of nuclear development, only to have that capability negated by the Gulf War; India, Pakistan, and North Korea, however, succeeded in declaring themselves in possession of nuclear weapons. The danger that “rogue states” and international terrorist organizations might attain and use nuclear weaponry came to loom large for America. 9/11 gave the G.W. Bush administration a sense of tremendous urgency in the matter of dealing with the issue of nuclear proliferation. Actually, the war against Iraq was waged under the pretext of eliminating weapons of mass destruction that Saddam Hussein allegedly had produced.<br>The proposal that H. Kissinger, G. Shultz, W. Perry and S. Nunn made in January 2007 calling for a world without nuclear weapons should be understood in this altered strategic context. Stressing the significance of coping with the threat of nuclear proliferation, these four highly prominent experts on nuclear strategy proposed the elimination of nuclear weapons. In the same vain, President Obama made a celebrated address in Prague in April 2009; his speech's major emphasis lay on nuclear disarmament and prevention of nuclear proliferation.<br>Nuclear weapons, which had brought about a certain stability and predictability in US-Soviet relations and helped insure Pax America, has now come to constitute the most pressing threat to US security. The nuclear proliferation is a disturbing legacy of the Cold War.