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.
Nuclear power by country
Nuclear power plants currently operate in 31 countries. 
Most are in Europe, North America, East Asia and South Asia.
The United States is the largest producer of nuclear power, while France has the largest share of electricity generated by nuclear power.
In 2010, before the Fukushima Daiichi nuclear disaster, it was reported that an average of about 10 nuclear reactors were expected to become operational per year, although according to the World Nuclear Association, of the 17 civilian reactors planned to become operational between 2007 and 2009, only five actually came on stream. 
Global nuclear electricity generation in 2012 was at its lowest level since 1999.
China has the fastest growing nuclear power program with 28 new reactors under construction, and a considerable number of new reactors are also being built in India, Russia and South Korea. 
At the same time, at least 100 older and smaller reactors will "most probably be closed over the next 10–15 years".