The U.S. and the Soviet Union conducted 434 open-air nuclear bomb tests from 1945 to 1963, according to data collected by the NRDC. Physicists and military engineers used the tests to study bomb types, sizes and destructive effects. Government leaders used nuclear tests as a diplomatic tool, flexing military muscle without conducting an attack.
As it became clear that nuclear fallout from the explosions was reaching civilian populations, the major world powers entered into arms-control negotiations that led to the 1963 Limited Test Ban Treaty, an early nuclear arms-control agreement between the U.S., U.S.S.R. and the U.K. The subsequent Comprehensive Nuclear Test Ban Treaty, which bans all nuclear explosions in all environments, was adopted by the UN General Assembly in September 1996 but hasn't been ratified by key nations including the U.S. and China.
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