The Cold War was a period of hostility between the United States and the Soviet Union from 1945-1991. The main reasons for the Cold War were the ideological differences between capitalism in the Western world led by the US and communism in the Eastern bloc led by the USSR. This led both sides to form military alliances and engage in a nuclear arms race in a strategy known as containment and brinkmanship to influence other countries and prevent the spread of the opposing system. The Cold War ended in the late 1980s as communism fell in Eastern Europe.