NATO was formed in 1949 by the United States in response to fears about Soviet control over Eastern Europe following World War II. It was intended as a defensive alliance between North American and Western European countries. In 1955, the Soviet Union responded by forming the Warsaw Pact, a defensive alliance between Eastern European countries and the Soviet Union, in order to counter NATO's inclusion of West Germany and perceived threat against Soviet control. Both alliances contributed to increased tensions and an arms race between the U.S. and USSR during the Cold War.