In 1948, it was decided to unite the American, British and French occupation zones in Germany. They did the same in Berlin, so West Berlin became a capitalist island inside the Soviet zone. Stalin tried to take over West Berlin by blocking all traffic, preventing food and supplies of entering West Berlin. The USA responded to this Berlin Blockade by starting an airlift: over the next three hundred days, thousands of Allied airplanes flew to West Berlin and landed food and fuel supplies there. Eventually the blockade was lifted. Because of this crisis, the USA and Western Europe formed the North Atlantic Treaty Organisation (NATO). The members of this Euro-American alliance agreed to support each other if one of them was attacked by another country. The Soviet Union responded by creating the Warsaw Pact, a similar military alliance of the Soviet Union and the Eastern Bloc countries.