The Potsdam Conference divided Germany into four occupied zones after World War II. Berlin was also divided. In 1948, the western zones formed West Germany in response to the Soviets refusing to end their occupation. The Cold War began as the US and USSR competed for influence, with the US pursuing containment and the USSR establishing satellite states in Eastern Europe. The Berlin Airlift provided supplies to West Berlin when it was blockaded. NATO and the Warsaw Pact formed military alliances on either side of the Iron Curtain dividing Europe. The Cold War then spread to Asia as communism took hold in China and the Korean War began.