jaykay,
You're referring to the Mongols doing that to Tibet in the 13th century? Or the Tibetans doing it to large parts of China in the 7th Century? Or the Nepalese doing it to Tibet in the 18th Century? Or the British in the early 20th Century?
Wikipedia has some good articles on this whole issue.
Tibetan sovereignty debate - Wikipedia, the free encyclopedia for example.
