[Manthink]

The question is highly relevant for at least two reasons. First, if, Tibet is under unlawful Chinese occupation, Beijing's legal-scale transfer of Chinese settlers into Tibet is a serious violation of the fourth Geneva Convention of 1949, which prohibits the transfer of civilian population into occupied territory. Second, if Tibet is under unlawful Chinese occupation, China's illegal presence in the country is a legitimate object of international concern.

Errr... Not sure where you got that info from...But I know the opposite is true. Did you know the UN and yes including India says Tibet is part of China ? 

So where is that "unlawful" part ? 

https://timesofindia.indiatimes.com/pm-o.../41145.cms