I recently posted about a documentary on precisely this topic. Please do yourself a favor and watch it as soon as possible. Be sure to watch both parts as the first deals mainly with the situation before the liberation while the second goes into the actual process of how the liberation happened. You don’t need to take our word for it, listen to what people who were alive back then had to say and what they wrote.

The documentary references many western sources (too many for my liking in fact, i would prefer a less eurocentric view) both contemporary as well as modern, including some that have very little reason to be sympathetic to communists and some that were probably outright racists and sinophobes, and even these paint a very grim picture of pre-liberation Tibet. It also lets Tibetans themselves tell their stories. So it is by no means presenting an exclusively Han Chinese perspective.

If you still have questions, reservations or concerns afterwards there are more resources that we can recommend to you on this subject.