world war II ended after the U.S. employed a newly developed weapon which changed the course of international relations; the atomic bombs dropped on Hiroshima and Nagasaki ended the war, but began a new 'Cold War' with America's ideological opposite the Soviet Union. Both the U.S. and the Soviet Union (the 'superpowers') waged 'proxy' wars, but avoided military conflict. the United States supported any government or regime which opposed communism, and sought to promote democracy to isolate communist regimes.