After the end of the war, the pre-1938 Czechoslovakia was reestablished, with the exception of Carpathian Ruthenia, which became part of the Ukrainian SSR (A Republic of the Soviet Union). From 1948 to 1989, Czechoslovakia was part of the Eastern Bloc with a command economy. Its economic status was formalized in membership of Comecon from 1949 and its defense status in the Warsaw Pact of May 1955. A period of political liberalization in 1968, known as the Prague Spring, was violently ended when the Soviet Union, assisted by some other Warsaw Pact countries invaded Czechoslovakia. In 1989, as Marxist–Leninist governments and communism were ending all over Europe, Czechoslovaks peacefully deposed their socialist government in the Velvet Revolution; state price controls were removed after a period of preparation.