The correct answer is the dissolution of the Soviet Union.
Explanation: The dissolution of the Soviet Union took place gradually. The end of the USSR was not consolidated in 1991. It begins earlier. The Eastern European bloc begins its collapse years earlier from a process.
1991 is only symbolic as the final decree. The dissolution of the Soviet Union began, however, in 1985. Misplaced measures end up shaking up internal relations in the bloc.
In addition, historical factors that followed years later culminated in the endpoint of the USSR. The final decree was in 1991, when, finally, the fall and dissolution of the USSR was announced.