The Warsaw Pact was a treaty alliance of eight communist countries under the leadership of the Soviet Union which was formed several years after the end of World War II. Its true name was the Treaty of Friendship, Cooperation, and Mutual Assistance, and was ostensibly formed to protect its members from another attack from Germany as had occurred during the war. It was formed nine years after the war when the former West Germany (Federal Republic of Germany) joined the North Atlantic Treaty Organization (NATO.)Among its members were Albania, Poland, Bulgaria, Hungary, Poland, Romania and East Germany. Many historians believe that it was formed not so much as a defense against a future German invasion as a counter to the NATO alliance composed of Western ("free") Nations. Forces operating under the Pact's auspices were responsible for the invasion of Hungary in 1956 when that country attempted to withdraw from the alliance, and the invasion of Czechoslovakia in 1968. The Pact formally ended in 1991 with the collapse of communist governments in the member nations.