The unified command structure was born of the need to address changes wrought not only by America's rapid post-war demobilization but the end of the occupation of Germany in 1949. Questions arose over the U.S. commitment to the defense of Western Europe against the Soviet Union (USSR). Providing for the common defense was a great concern, especially after the Berlin Crisis of 1948–49 when the Soviet Union blocked access to the divided city and the U.S. and United Kingdom responded with an unprecedented airlift. In 1949 the allies established the North Atlantic Treaty Organization (NATO).