"The United States has been a leader of worldwide efforts to prevent the spread of nuclear weapons. To this end, the international community and many individual states have agreed to a range of treaties, laws, and agreements, known collectively as the nuclear nonproliferation regime, aimed at keeping nations that do not have nuclear weapons from acquiring them. The nonproliferation regime has also been concerned with preventing terrorists from obtaining a nuclear weapon or the materials to craft one. The attacks on New York and Washington September 11 added a new level of reality to the threat that terrorists might acquire a nuclear weapon and explode it in a populated area. Other nonproliferation concerns include a number of regional crisis points: the India- Pakistan arms race, North Korea, and the Middle East, primarily Iraq, Iran, and Israel. There is concern about China's actions in expanding its nuclear force, and of Chinese and Russian activities that may encourage proliferation in the other regions."
CRS Issue Brief for Congress, IB10091