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.
Treaty on the Prohibition of Nuclear Weapons
Among the countries voting for the treaty's adoption were South Africa and Kazakhstan, both of which formerly possessed nuclear weapons and gave them up voluntarily. Iran and Saudi Arabia also voted in favour of the agreement. There are indications that Saudi Arabia has financially contributed to Pakistan's atomic bomb projects and in return has the option to buy a small nuclear arsenal, an option that would be realized in the event that Iran obtains nuclear warheads.