Nuclear Non-Proliferation Treaty
The Nuclear Non-Proliferation Treaty (NPT) is a treaty, opened for signature on July 1, 1968, restricting the possession of nuclear weapons. The vast majority of sovereign states (189) are parties to the treaty.
Only five states are permitted by the NPT to own nuclear weapons: the United States (signed 1968), United Kingdom (1968), France (1992), Soviet Union (1968; since replaced by Russia), and the People's Republic of China (1992). These were the only states possessing such weapons at that time, and are also the five permanent members of the United Nations Security Council. These 5 Nuclear Weapons States (NWS) agree not to transfer nuclear weapons technology to other states, and the non-NWS state parties agree not to seek to develop nuclear weapons.
The 5 NWS parties have made undertakings not to use their nuclear weapons against a non-NWS party except in response to a nuclear attack, or a conventional attack in alliance with a Nuclear Weapons State. However, these undertakings have not been incorporated formally into the treaty, and the exact details have varied over time. The United States, for instance, has indicated that it may use nuclear weapons in response to an attack with non-nuclear "weapons of mass destruction", such as biological biological or chemical weapons, since the US may not use either of these in retaliation. United Kingdom Defence Secretary Geoff Hoon has also explicitly invoked the possibility of the use of the country's nuclear weapons in response to a non-conventional attack by "rogue states".
Article VI and the preamble indicate that the NWS parties pursue to reduce and liquidate their stockpiles. After more than 30 years this has remained only a promise. In Article I, the NWS declare not to "induce any non-nuclear-weapon State to ... acquire nuclear weapons". A preemptive-strike doctrine and otherwise threatening postures can be viewed as induction by non-NWS parties. Article X states that any state can withdraw from the treaty if they feel that "extraordinary events", for example a perceived threat, force them to do so.
Three states - India, Pakistan, and Israel - have declined to sign the treaty. All three possess nuclear weapons, which would be prohibited had any of them ratified the treaty. These countries argue that the NPT creates a club of "nuclear haves" and a larger group of "nuclear have-nots" by restricting the legal possession of nuclear weapons to those states that tested them before 1967, but the treaty never explains on what ethical grounds such a distinction is valid.
South Africa undertook a nuclear weapons program, allegedly with the assistance of Israel, and may have detonated a nuclear test over the Atlantic, but has since renounced its nuclear program and signed the treaty in the early 1990s after destroying its small nuclear arsenal. India and Pakistan have publicly announced possession of nuclear weapons, and have detonated nuclear tests. Israel has been developing nuclear weapons at its Dimona site in the Negev since 1958, and is believed to have stockpiled between 100 to 200 warheads. The Israeli government refuses to confirm or deny these claims, although this is now regarded as an open secret after scientist Mordechai Vanunu revealed the program to an English newspaper.
North Korea ratified the treaty, but revoked its signature after a dispute with inspectors over inspections of non-declared nuclear facilities. Iran also signed, but, as of 2004, is under suspicion of having violated the treaty through an active program to develop nuclear weapons. The International Atomic Energy Agency (IAEA), the UN's nuclear regulatory body, is investigating.
In August 2004, United States intelligence officials and non-governmental experts concluded that diplomatic efforts to prevent the proliferation of nuclear weapons to Iran and North Korea have failed to slow their weapons development programs. 
The major loophole in the NPT is that uranium enrichment can be used for fuel reasons. This is only a small step away from developing nuclear warheads, and this can be done in secret or by withdrawing from the NPT (like North Korea). So at the moment, the only barrier to missile construction is political will. Mohamed ElBaradei, the head of the IAEA has said that if they wanted to, 40 countries could develop nuclear missiles. The NPT treaty parties meet next in May 2005 in a Review Conference (which happens every five years).
The parties to the treaty are:
- North Korea and weapons of mass destruction
- Iran's nuclear program
- 13 steps (an important section in the Final Document of the 2000 Review Conference of the Treaty)
- nuclear proliferation