The Atomic Age, also known as the Atomic Era, is the period of history following the detonation of the first nuclear ("atomic") bomb, Trinity, on July 16, 1945, during World War II. Although nuclear chain reactions had been hypothesized in 1933 and the first artificial self-sustaining nuclear chain reaction (Chicago Pile-1) had taken place in December 1942, the Trinity test and the ensuing bombings of Hiroshima and Nagasaki in Japan that ended World War II represented the first large-scale use of nuclear technology and ushered in profound changes in sociopolitical thinking and the course of technology development. Atomic power was seen to be the epitome of progress and modernity.