The disintegration of the Soviet Union in 1991 was caused by a mix of internal problems and external pressures. Economic decline, political rigidity, rising nationalism, and the unintended effects of Gorbachev’s reforms all contributed to its collapse.

1. Economic Stagnation: The Soviet economy had become inefficient due to central planning, leading to shortages and poor living standards. Excessive military spending further strained resources, and the growing gap with the West became clear.

2. Political Limitations: The one-party Communist rule restricted freedoms and citizen participation. Widespread censorship and an unaccountable, inefficient bureaucracy led to public disillusionment.

3. Rise of Nationalism: Nationalist movements gained strength in several republics like Ukraine, Georgia, and the Baltic states. These regions sought autonomy and eventually independence, fueled by feelings of unequal treatment.

4. Gorbachev’s Reforms: Policies like Perestroika (economic restructuring) and Glasnost (openness) aimed to modernize the system but instead weakened central control. Glasnost encouraged criticism of the regime, and Perestroika brought instability without real improvement.

5. External Pressures: The Cold War arms race and the war in Afghanistan drained resources. The fall of communist regimes in Eastern Europe further signaled the Soviet model’s failure.

Conclusion: The USSR collapsed due to a combination of economic failures, political repression, nationalist movements, reform-induced instability, and global pressures. It could not adapt to the changing world, leading to its ultimate breakdown.