The Nuclear Non-Proliferation Treaty (NPT) is the single most important legal tool that the world has to try to stop the spread of nuclear weapons.
It was conceived in the 1960s, when many world leaders feared that nuclear weapons would spread to as many as 25 nations. And the treaty has helped to limit their spread. But nuclear weapons have proliferated nevertheless. Three states with the bomb remain outside the treaty, and several of those states that signed it have cheated.
The NPT was negotiated in 1968, with the United States becoming one of the first to sign. It was ratified and went into force in 1970, initially with a term of twenty-five years. In 1995, all the signatories of the treaty came together at the United Nations in New York and extended the its term indefinitely.
A total of 188 nations have now signed the treaty.
It divides the world into nuclear weapons haves and have-nots, based solely on the world that existed in 1968. Then only the United States, the Soviet Union, Great Britain, France and China had acquired nuclear weapons. The treaty recognizes them as the only legal nuclear weapons states.
The rest of the signatories were required to pledge not to acquire nuclear weapons. But in exchange, the treaty acknowledges their right to peaceful nuclear energy. And the nuclear weapons states pledge that at some future point, they will give up their nuclear arsenals.
Known and Suspected Nuclear Powers
The United States and Russia have the largest nuclear arsenals, each at the moment with an estimated 3,000 deployed nuclear weapons. The most recent agreement between Washington and Moscow, in 2002, requires each to reduce its deployed nuclear weapons to roughly 2,000 by the year 2012.
France is believed to have some 400 warheads, China 300 and Great Britain about 200.
Three nations possess nuclear weapons and are outside the treaty, that is, they have never signed it. They are India, Pakistan and Israel. The NPT requires its signatories to refuse civil nuclear cooperation with states that have refused to sign.
There are two other problem nations. North Korea signed the treaty in the early 1990s, but Pyongyang cheated and developed a secret nuclear weapons program. It froze that program in 1995, but it withdrew from the treaty in 2003 and restarted its nuclear weapons program. North Korea may have manufactured as many as six nuclear weapons.
Iran is also an NPT signatory, but it developed a nuclear program in secret. Iran's leaders insist it is purely civilian in nature, but many suspect Iran of seeking nuclear weapons. Right now, there is no evidence that Iran possesses a nuclear bomb.