Nuclear proliferation is the increasing worldwide availability of nuclear weapons, nuclear knowledge, and nuclear materials such as enriched uranium or plutonium. It has long been a stated concern of politicians and nuclear arms control advocates, though the actual effort devoted to such goals has varied. Nuclear weapons technology was first developed by the Manhattan Project of the United States in July 1945.
Watchdog groups seek to minimize the accessibility of nuclear weapons, materials, and knowledge in an effort to lower the probability of nuclear war, and/or take steps towards the relinquishment of nuclear weapons entirely. Most calculations have shown that even a limited nuclear war could kill millions of people and disrupt agriculture worldwide, while an all-out nuclear war could kill hundreds of millions and end civilization as we know it.
Since nuclear weapons were developed in 1945, about a dozen countries have pursued the technology. After the United States' atomic bomb Trinity, the former Soviet Union achieved success in 1949 (RDS-1), followed by the United Kingdom in 1952 (Hurricane), France in 1960 (Gerboise Bleue), China in 1964 (596), India in 1974 (Smiling Buddha), Pakistan in 1998 (Chagai-I), and North Korea in 2006 (Kim-Il Sung's Return). Israel likely developed nuclear weapons in 1979 (possibly related to the Vela Incident), and the country is widely thought to possess nuclear weapons, but it is undeclared. Through the breakup of the Soviet Union in 1991, several smaller states (Ukraine, Belarus and Kazakhstan) acquired nuclear materials, weapons, and knowledge.
Thought on the prevention of nuclear proliferation is heavily dictated and influenced by the Nuclear Non-Proliferation Treaty, which was opened for signature on 1 July 1968 and has since been signed by 189 countries, including the five "official" nuclear weapons states: the US, UK, France, Russia, and China. The few countries that have not signed the treaty include Israel, Pakistan, India, and Myanmar. Many countries and observers have argued that the treaty is ineffective, partially because it is biased towards certain countries in that some are allowed nuclear weapons and some are not. Also at issue is the claim of NATO countries, especially the United States, that the treaty would be suspended in the case of "general war," which seems to render the treaty moot with regards to one of the major issues it was created to solve.
There is a major disagreement in the international community regarding the way that nuclear nonproliferation efforts should move forward. The United States emphasizes the prevention of nuclear weapons being acquired by so-called "rogue states" like North Korea and Iran, whereas most other countries emphasize the need for the existing nuclear powers to disarm and lower their stockpiles. In light of continuing tensions between Russia and NATO, this seems unlikely to occur in the foreseeable future.