Some five decades ago, world leaders came together on an urgent mission to avert "the devastation that would be visited upon all mankind" in the event of a nuclear war. The five then-existing nuclear weapon states - the United States, Soviet Union (now Russia), United Kingdom, France and China - signed the international nuclear Non-Proliferation Treaty (NPT). They agreed to negotiate in good faith to end the nuclear arms race at an early date and to achieve a world without nuclear weapons.