The Warsaw Pact included the USSR and the countries of Eastern Europe: Albania, Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, Romania.
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The Warsaw Pact was given that name because the agreement was signed in Warsaw, Poland. Established in 1955, the Warsaw Pact included the Soviet Union and satellite communist nations in Eastern Europe (Albania, Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, Romania). The nations signing the treaty called on each other to defend of any member of the Pact that was threatened by enemy forces. The formation of the Warsaw Pact was in direct response to the formation of the North Atlantic Treaty Organization (NATO).
In 1958, Hungary tried to withdraw from the Warsaw Pact, but Soviet troops came in and crushed the movement in Hungary and replaced the government.
Albania withdrew from the Warsaw Pact in 1968, after relations between Albania and the USSR had split beginning in 1961.
The Warsaw Pact formally dissolved in 1991, following the overthrow of communist governments in Eastern Europe and while the USSR itself was proceeding toward its own dissolution later that year.