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.
Historical nuclear weapons stockpiles and nuclear tests by country
North Korea joined the nuclear club in 2006 or before. A United States Defense Intelligence Agency report from 1999 projected that both Iran and Iraq would join the nuclear club and have 10-20 nuclear weapons in 2020. However, it is worth pointing out that this report was written before the overthrow of Iraqi dictator Saddam Hussein and before information was released indicating that Iraq had already given up its nuclear weapons program. Even before the U.S. started the nuclear club in 1945, some states (most notably Germany) unsuccessfully attempted to build nuclear weapons.