Soviet revisionism
Soviet revisionism was a successful movement of the Soviet bourgeoisie to restore capitalism in the USSR, which disguised itself as communist. The turning of the USSR into a revisionist state was put in place upon Stalin's death, in 1953. At that point, Nikita Khrushchev took power and started tearing away at the foundations of Marxism-Leninism while letting criminals run free and defaming Stalin. At first he started with the intensification of class struggle under socialism, saying that class struggle had ended and that the Soviet Union was now an "all-people's state" instead of a dictatorship of the proletariat. It is known to Marxists worldwide that the state exists only as a weapon of one class against another.
The next revisionist premier, Leonid Brezhnev, continued the plan with market reforms known as perestroika and a movement to allow counter-revolutionaries to openly spread feudal-bourgeois propaganda called glasnost. However, glasnost wasn't that important, considering feudal-bourgeois propaganda was already being disseminated from the Communist Party itself, which at had openly admitted to not being a dictatorship of the proletariat long before this.
Finally, there was Gorbachev, who let criminals out of prison, illegalized the Communist Party, and oversaw the official dissolution of the Soviet Union.