The atomic bomb that the US dropped on Hiroshima ended World War II, but it also ushered in the nuclear age -- a tense era dominated by the Cold War. As the Soviet bloc and the Western allies (led by the US) each tried to make the world conform to their politicoeconomic system, the shadow of the bomb that might end civilization hung over all. Yet the era was also filled with exciting developments in science and the arts as well as movements for social equality and democratic governments worldwide.