The six Warsaw Pact countries of Eastern Europe, while nominally independent, were widely recognized in the international community as the Soviet satellite states. All had been occupied by the Soviet Red Army in 1945, had Soviet-style socialist states imposed upon them, and had very restricted freedom of action in either domestic or international affairs. Any moves towards real independence were suppressed by military force – in the Hungarian Revolution of 1956 and the Prague Spring in 1968. Gorbachev abandoned the oppressive and expensive Brezhnev Doctrine, which mandated intervention in the Warsaw Pact states, in favor of non-intervention in the internal affairs of allies – jokingly termed the Sinatra Doctrine in a reference to the Frank Sinatra song "My Way".

What year did the Prague Spring take place?