Warsaw Pact (formally the Warsaw Treaty of Friendship, Cooperation, and Mutual Assistance), military alliance of seven European Communist countries, formed to counter the rearmament of West Germany, officially called the Federal Republic of Germany (FRG), and its admission to the North Atlantic Treaty Organization (NATO). The treaty was signed in Warsaw, Poland, on May 14, 1955, by Albania, Bulgaria, Czechoslovakia (now the Czech Republic and Slovakia), East Germany (now part of the united Federal Republic of Germany), Hungary, Poland, Romania, and the Union of Soviet Socialist Republics (USSR). The alliance was dominated by the USSR, which kept strict control over the other countries in the pact. In 1961 Albania broke off diplomatic relations with the USSR because of ideological differences and in 1968 withdrew from the pact.
From the mid-1950s through the 1980s, two major bodies carried out the functions of the Warsaw Pact: the Political Consultative Committee and the Unified Command of Pact Armed Forces, both based in Moscow. Under the terms of the treaty, the Political Consultative Committee coordinated all activities, except those purely military, and the Unified Command of Pact Armed Forces had authority over the troops assigned to it by member states. It was agreed that the supreme commander would be from the USSR. The Warsaw Pact's only military action was directed against Czechoslovakia, a member state. (In the autumn of 1956, the USSR took unilateral military action against Hungary, another Warsaw Pact member state, killing thousands of Hungarians and causing 200,000 to flee the country.) In August 1968, after the Czech government enacted reforms offensive to the USSR, forces of the USSR, Poland, Hungary, East Germany, and Bulgaria invaded Czechoslovakia and forced a return to a Soviet-style system. Romania opposed the invasion and did not participate, but remained a member of the Pact.
Although the Warsaw Pact was officially renewed in 1985 for another 20 years, the political transformation of Eastern Europe at the end of the 1980s profoundly weakened the organization. The USSR began withdrawing its troops from other Warsaw Pact countries, and East Germany pulled out to join West Germany as the reunified nation of Germany in October 1990. All joint military functions ceased at the end of March 1991, and in July leaders of the remaining six member nations agreed to dissolve the alliance.