NON-PROLIFERATION OF NUCLEAR WEAPONS, TREATY ON THE

also called Nuclear Non-proliferation Treaty, agreement of July 1, 1968, signed by the United Kingdom, the United States, the Soviet Union, and 59 other states, under which the 3 major signatories agreed not to assist states not possessing nuclear explosives in obtaining or producing them. The treaty became effective in March 1970 and was to remain so for a 25-year period. Additional nations later ratified the treaty, including the world's two other major nuclear powers, France and China, in 1992. The treaty was extended indefinitely in 1995 by a consensus vote of 174 countries at the United Nations headquarters in New York.