At the end of the war the Soviets controlled much of Eastern Europe and installed communist ideas from spreading. It helped Western European countries to stay free and also gave them big sums of money to help rebuild their weak economies. In 1949 the United States and other western countries founded NATO (the North Atlantic Treaty Organization), on the other side the Soviet led the Warsaw Pact, a military organization of eastern European countries. In the 1950s many East Berliners moved to West Berlin to escape Communism.