What is the best explanation for the collapse of the Soviet union?

There are a few key factors that are commonly cited as contributing to the collapse of the Soviet Union:

1. Economic issues: The Soviet economy was stagnating and unable to keep up with the technological advancements of Western countries. The centrally planned economy proved to be inefficient and inefficient, leading to widespread shortages of consumer goods and a lack of innovation.

2. Political reforms: The policies of perestroika (restructuring) and glasnost (openness) implemented by Soviet leader Mikhail Gorbachev in the late 1980s allowed for greater political freedoms and transparency, but also led to increasing unrest and calls for independence from Soviet republics.

3. Nationalism: Nationalist movements within the various Soviet republics, particularly in the Baltic states, Ukraine, and the Caucasus region, sought greater autonomy and eventual independence from the Soviet Union.

4. Military overextension: The Soviet Union's costly involvement in the war in Afghanistan and the arms race with the United States strained the country's resources and contributed to its economic decline.

5. Collapse of the Eastern Bloc: The fall of the Berlin Wall in 1989 and the subsequent collapse of communist regimes in Eastern Europe weakened the Soviet Union's influence in the region and emboldened nationalist movements within the Soviet republics.

Overall, a combination of economic, political, and social factors led to the collapse of the Soviet Union in 1991, marking the end of the Cold War.