To end World War II the United States dropped two atomic bombs on the cities of Hiroshima and Nagasaki in Japan in August 1945, causing many thousands of casualties. To this date, the US is the only country to ever have used nuclear weapons.
For a few years after the war the US was sole country possessing nuclear weapons. In 1949, the Soviet Union became a nuclear power, which started the Cold War and a nuclear arms race between the two superpowers. The other three permanent members of the United Nations Security Council also developed their own nuclear weapons. The United Kingdom tested its first nuclear weapon in October 1952, France followed suit in 1960 and the People’s Republic of China successfully detonated its first atomic bomb in 1964.
The fragile relation between the US and the Soviet Union gave rise to the idea that the world would be more safe and secure without the further spread of nuclear weapons. More nuclear players would mean less global security, because this would increase the risk of miscalculation, accidents, unauthorised use of weapons and tension escalation. This was the impetus behind the Non Proliferation Treaty, initiated by the neutral countries Ireland and Finland.
The Treaty on the Non-Proliferation of Nuclear Weapons (NPT) was designed to limit the spread of nuclear weapons. The NPT is interpreted as a three-pronged approach to non-proliferation, disarmament and the right to the peaceful use of nuclear technology. It came into force in 1970, initially for the duration of 25 years. During a Review Conference in 1995, however, the signing parties decided by consensus to extend the treaty indefinitely and without conditions.
Nearly all UN members have signed the treaty. The five permanent members of the UN Security Council are recognised as nuclear weapon states. Four non-parties to the treaty are known or believed to possess nuclear weapons: India, Pakistan and North Korea have openly tested and declared that they possess nuclear weapons. India exploded its first nuclear device in 1974, Pakistan following suit in 1998. North Korea withdrew from the treaty in 2003. Israel, the fourth county, has been conducting a smokescreen policy regarding the possession of nuclear weapons. This has never been confirmed nor denied.