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 weapons of the United States
The United States is one of the five nuclear weapons states with a declared nuclear arsenal under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), of which it was an original drafter and signatory on 1 July 1968 (ratified 5 March 1970). All signatories of the NPT agreed to refrain from aiding in nuclear weapons proliferation to other states.