The attack on Hiroshima in 1945 triggered a nuclear arms race. The U.S. monopoly on nuclear weapons did not last long. The Soviet Union successfully tested an atomic bomb in 1949, followed by Britain in 1952, France in 1960, and China in 1964. The Nuclear Non-Proliferation Treaty (NPT) came into effect in 1970, and had been ratified by 189 countries as of December 2004. However, a number of countries that have not signed the NPT do possess nuclear weapons: India (1974), Pakistan (1998), and Israel (?). The South African government announced in 1993 that it had dismantled its nuclear arsenal. In 2003, North Korea announced its withdrawal from the NPT and made statements to the effect it was already in possession of nuclear weapons.

    After World War II, efforts were made to impede the unlimited development of nuclear weapons. The United States and the Soviet Union concluded the Partial Test Ban Treaty in 1963, while the two countries and Britain signed the NPT in 1968. The United States and the Soviet Union commenced the first round of Strategic Arms Limitation Talks (SALT I) in 1972, and signed a second Strategic Arms Reduction Treaty (START II) in 1993, which has not come into effect. The NPT was extended indefinitely in 1995. In 2001, the United States and Russia agreed to reduce their strategic nuclear weapons by about two-thirds. However, the current number of nuclear weapons stockpiled or deployed around the world is sufficient to kill the world's population several times over.
    Development of nuclear weapons also shifted from the atmosphere to underneath the Earth's surface. Competition is underway to develop nuclear weapons without the aid of nuclear tests now that sub-critical computer simulations are possible.

    Moreover, the danger of nuclear proliferation no longer comes from states alone. Measures are necessary to address the "nuclear black market". Efforts are currently underway to establish multilateral controls over such as activities as uranium enrichment and plutonium extraction. An advisory panel in the International Atomic Energy Agency (IAEA) unveiled such proposals in February 2003, which were submitted to the NPT Review Conference in New York in May 2005.
    However, five countries - the United States, Britain, France, Russia, and China - are not obliged to undergo IAEA inspections. India, Pakistan, and Israel have not joined the NPT, while North Korea has withdrawn from the pact. Nor has the NPT been effective in the case of Iran.

Most of the Southern Hemisphere now a Nuclear-Weapon-Free Zone
    Nuclear-Weapon-Free Zone treaties, which ban the manufacture, testing, stationing and use of nuclear weapons within a specific region, by both the countries inside the region and outside nuclear powers, were established for Antarctica in 1959, outer space in 1967, and the seafloor in 1971. The Cuban Missile Crisis prompted the conclusion of a Nuclear-Weapon-Free Zone Treaty for Latin America in 1967, whilst similar treaties were established for the South Pacific in 1985, Southeast Asia in 1995, and Africa in 1996, so that most of the Southern Hemisphere is now a Nuclear- Weapon-Free Zone (the four zones cover 108 countries). However, these treaties cannot be truly effective without the participation of the nuclear powers.

    The IAEA Director General Dr. Mohamed El Baradei called for the establishment of nuclear-free zones in the Middle East and the Korean Peninsula at the NPT Review Conference in May 2005. The world still lives in fear of nuclear weapons, despite signs of hope.