Chinese repression happened. Understand why though. A huge amount of the water that finds its way into China's central valley comes from the Himalayas and rivers with sources that originate in Tibet. They have to have control over the full length of those rivers so they have control over their water supply.

This is the same lesson the Egyptians are learning. The Nile is a very long river and has a source in the highlands of the Eastern Horn of Africa. Ethiopia keeps damming up the river for hydroelectric power and the result is that they're also throttling the water that gets to Egypt. Egypt has for millennia relied upon those waters and their seasonal floods. The silt in those floods is fertilizer for the entire Nile delta. The dams are blocking all that up, and Egypt has no control over it because the dams are built in other countries. China is damn sure not going to allow that to happen to them.

So, Tibet's never going to be free of China. China is dependent on that never happening.