The main reasons for the upheaval in Eastern Europe and the collapse of the Soviet Union are as follows:
Historical reasons: After the communist parties of the Eastern European countries came to power, they all copied the Soviet model and were to a large extent subject to the Soviet Union, and the Soviet Union forced the Eastern European countries to align their domestic and foreign policies with it. In fact, the countries of Eastern Europe did not have the right to become independent.
Internal reasons: The Soviet Union abandoned the socialist road, the proletariat, the leadership of the Communist Party, Marxism-Leninism, and blamed the individual leaders for the mistakes in socialist construction and party building, and developed the correction of the leaders' mistakes into a complete negation of the history of struggle of the CPSU.
External causes: The strategy of peaceful evolution pursued by imperialism was the external cause of the drastic changes in the Soviet Union and Eastern Europe, and the Western countries carried out ideological infiltration of socialist countries through personnel exchanges, project cooperation, and propaganda offensives.
Economic reasons: Since the 80s, the debt problems of the Eastern European countries have been very serious, and by the 88 years they had greatly exceeded the internationally recognized standard line of external debt security. The imbalance between production and consumption led to a complete collapse of the economy.
Political reasons: The leaders of the ruling parties in the Soviet Union and the countries of Eastern Europe were confused ideologically, at a loss in practice, and in theory on such important issues as "how to carry out reforms," "what are the directions and goals of reform," and "how the socialist system should be consolidated and developed."
All of these factors combined to lead to the upheavals in Eastern Europe and the collapse of the Soviet Union.