After WWII, Western Europe was occupied by the U.S., France, and UK while Eastern Europe, including parts of Germany, was occupied by the Soviet Union. Germany's capital, Berlin, was divided among the occupying countries. This led to the formation of opposing military alliances - NATO among Western countries and the Warsaw Pact among Eastern European countries behind the Iron Curtain. The division of Europe grew during the Cold War period of political and economic tensions between the capitalist West and communist East.