United States and weapons of mass destruction
The United States is known to have possessed three types of weapons of mass destruction: nuclear weapons, chemical weapons, and biological weapons. The U.S. is the only country to have used nuclear weapons in combat, when it detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki during World War II. It had secretly developed the earliest form of the atomic weapon during the 1940s under the title "Manhattan Project". The United States pioneered the development of both the nuclear fission and hydrogen bombs (the latter involving nuclear fusion). It was the world's first and only nuclear power for four years (1945–1949), until the Soviet Union managed to produce its own nuclear weapon. The United States has the second largest number of deployed nuclear weapons in the world, after Russia.
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.