Why did the Soviet Union disintegrate? What is the most fundamental reason?

Economic collapse, highly centralized political and economic system and sharp ethnic contradictions can all be attributed to historical problems and Gorbachev's political reform, which made the party lose its ruling ability. In fact, the deep-seated reason is that the Soviet system can't keep up with the changes of the times, leading to economic collapse. At the same time, it hastily reformed politics. Once the party loses its ruling power, it is all over.