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.
Prior to the beginning of the Second World War, the First World War (1914–1918) was believed to have been the "war to end all wars," as it was popularly believed that never again could there possibly be a global conflict of such magnitude. During the inter-war period between the two World Wars, WWI was typically referred to simply as "The Great War". The outbreak of World War II in 1939 disproved the hope that mankind might have already "outgrown" the need for such widespread global wars.
With the advent of the Cold War in 1947 and with the spread of nuclear weapons technology to the Soviet Union, the possibility of a third global conflict became more plausible. During the Cold War years the possibility of 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. At the height of the Cold War, a scenario referred to as MAD (Mutually Assured Destruction), had been calculated which determined that an all-out nuclear confrontation would most certainly destroy all or nearly all human life on the planet. The spectre of the potential of the absolute destruction of the human race may have contributed to the ability of both American and Soviet leaders to avoid such a scenario.
