The USSR and seven other European countries signed the Treaty of Friendship, Cooperation, and Mutual Assistance better known as the Warsaw Pact.
The Warsaw Pact was established shortly after West Germany was admitted to NATO. The USSR was concerned by the remilitarisation of West Germany, something it had tried to avoid when it proposed a new European Security Treaty that failed to gain support from the Western powers in November 1954.
Just five days after West Germany joined NATO representatives of the Soviet Union, Albania, Poland, Romania, Hungary, East Germany, Czechoslovakia, and Bulgaria met in Warsaw where they signed the treaty. While the agreement established a system of collective security between the member states it also set up a unified military command under the leadership of the Soviet Union.
The Pact permitted Soviet troops to be garrisoned on satellite territory, consequently strengthening Soviet control over the Eastern Bloc and acting as a military counterpart to Comecon, the socialist economic organisation that had been established in 1949.
The presence of Soviet troops was a contributing factor to the 1956 uprisings in both Hungary and Poland. Both these countries did, however, take part in the Warsaw Pact invasion of Czechoslovakia in 1968 that ended the Prague Spring. Only Romania and Albania refused to join the invasion, the latter subsequently withdrawing completely from the pact.
The Warsaw Pact was formally declared “nonexistent” on 1 July 1991, although in practice it had been in decline for two years as a result of the overthrow of communist governments in the member states that had begun in 1989.