World War III (WWIII or WW3) and Third World War are names given to a hypothetical third worldwide military conflict subsequent to World Wars I and II. The term has been in use since the end of World War II, and was also applied somewhat sarcastically, to describe broad conflicts indirectly involving many countries from different parts of the world, such as the Cold War or the War on Terror.
Because of the development and use of nuclear weapons near the end of World War II and their subsequent acquisition and deployment by many countries, the potential risk of a nuclear devastation of Earth’s civilization and life is a common theme in speculations of a Third World War. Another major concern is that biological warfare could cause a very large number of casualties, either intentionally or inadvertently by an accidental release of a biological agent, the unexpected mutation of an agent, or its adaptation to other species after use. High-scale apocalyptic events like these, caused by advanced technology used for destruction, could
potentially make Earth’s surface uninhabitable, what prompts many to believe that after the war,
humans would live either in underground facilities or in colonies in the space (like in the Moon or Mars or a space vehicle).
World War I (1914–1918) was regarded at the time as the “war to end all wars,” as it was believed there could never again be another global conflict of such magnitude. World War II (1939–1945) proved that to be false, and with the advent of the Cold War in 1947 and the adoption of nuclear weapons, the possibility of a third global conflict became more plausible. The perceived threat then decreased with the end of the Cold War in 1991 when the Soviet Union collapsed, leaving the United States as the sole global superpower. A Third World War was anticipated and planned for by military and civil authorities in many countries. Scenarios ranged from conventional warfare to limited or total nuclear warfare.