The idea for a treaty to prevent the spread of nuclear weapons to more countries was supported unanimously by the UN General Assembly in 1961. At that time, only Britain, France, the Soviet Union and United States had tested nuclear weapons. Then China did in 1964. These five States became the five States permitted by the Nuclear Non-Proliferation Treaty (NPT) to have nuclear weapons - until a future day when nuclear disarmament could be negotiated. They were already the Permanent Five (P-5) members of the UN Security Council.
Negotiations toward the NPT were led by the Soviet Union and the United States but included the other members of the Eighteen Nation Disarmament Conference - allies of the two plus India and the seven other non-aligned members. The resulting treaty was signed in 1968.
The NPT permits the P-5 to have nuclear weapons. All other NPT signatories are "non-nuclear-weapon States" who are prohibited from acquiring nuclear weapons. To gain their signatures, the NPT promises assistance to them in the peaceful uses of nuclear energy and negotiations toward nuclear disarmament. As IAEA Director General Mohamed ElBaradei said recently: "The NPT contains a triangular linkage: verified nuclear non-proliferation; cooperation in peaceful uses of nuclear energy; and nuclear disarmament. Without this linkage, there would have been no agreement on the NPT in 1968.
Besides the P-5, the treaty now has 184 countries that have promised not to have nuclear weapons and that have agreed to accept inspections by the IAEA to verify that they are carrying out their promises. However, India, Pakistan, and Israel refused to join the treaty, and the Democratic People´s Republic of Korea (North Korea) withdrew from it.
As one of the negotiators of the NPT, I can remember the vigorous participation of India in the debates at the Geneva disarmament conference over the treaty. Some of the language of the treaty came from India. At first I expected India to join, but, after several years of attempts to persuade it to do so, it became clear it would not. Pakistan had not been one of the negotiating parties, but did not join after its rival India refused to do so. The US negotiated with Israel during the 1960s in an attempt to persuade it not to seek nuclear weapons, but to no avail. The Soviet Union persuaded North Korea to join, but North Korea delayed signing an inspection agreement with the IAEA for years, and then, after signing one, refused to give IAEA inspectors access to all its nuclear activities. In 2003, it announced its withdrawal from the NPT. Of these four countries, only India and Pakistan have tested nuclear weapons. Israel and North Korea are assumed to have them.