Weapon of mass destruction
The only country to have used a nuclear weapon in war is the United States, which dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki during World War II. There are eight countries that have declared they possess nuclear weapons and are known to have tested a nuclear weapon, only five of which are members of the NPT. The eight are China, France, India, North Korea, Pakistan, Russia, the United Kingdom, and the United States.
Nuclear proliferation
India, Pakistan and Israel have been "threshold" countries in terms of the international non-proliferation regime. They possess or are quickly capable of assembling one or more nuclear weapons. They have remained outside the 1970 NPT. They are thus largely excluded from trade in nuclear plant or materials, except for safety-related devices for a few safeguarded facilities.