World War III

World War III, also known as the Third World War, is a hypothetical future global conflict subsequent to World War I (1914–1918) and World War II (1939–1945). It is widely predicted that such a war would involve all of the great powers, like its two predecessors, and the use of nuclear weapons or other weapons of mass destruction, thereby surpassing all prior conflicts in scale, devastation, and loss of life.

World War III was initially synonymous with the escalation of the Cold War (1947–1991) into conflict between the US-led Western Bloc and Soviet-led Eastern Bloc, though the United States and the Soviet Union never directly engaged. Since the United States' development and use of nuclear weapons in the atomic bombings of Hiroshima and Nagasaki at the end of World War II, the risk of a nuclear apocalypse causing widespread destruction and the potential collapse of modern civilization or human extinction has been central in speculation and fiction about World War III. The Soviet Union's development of nuclear weapons in 1949 spurred the nuclear arms race and was followed by several other countries.

Regional proxy wars, including the Korean War (1950–1953), Vietnam War (1955–1975), and Soviet–Afghan War (1979–1989), while significant, did not lead to a full-scale global conflict. Such a conflict was planned for by military and civil personnel around the world, with scenarios ranging from conventional warfare to limited or total nuclear warfare. The certainty of escalation from one stage to the next was extensively debated. For example, the Eisenhower administration promulgated a policy of massive retaliation with nuclear forces in response to a minor conventional attack. After the Cuban Missile Crisis in 1962, which brought the U.S. and Soviet Union to the brink of war, the strategic doctrine of mutually assured destruction, which held that a full-scale nuclear war would annihilate all parties, became widely accepted. At the 1985 Geneva summit, U.S. and Soviet leaders first jointly stated "a nuclear war cannot be won and must never be fought".