What claim did China use to justify invading Tibet in 1950?

The claim that China used to justify invading Tibet in 1950 is that Tibet was formerly under the rule of China and so it has all the rights to rule over it.

Explanation:

On 7 October 1950, The Communist Party of China, declared that Tibet should again be made an integral part of China. This led to the Chinese invasion in Tibet thus increasing the cross - border tensions and territorial disputes.

Around 1.6 million of Tibetans were estimated to be killed by china so far.

The lack of the agreement of the various sides as to terminology highlights that the "serfdom in Tibet" controversy is a politicized debate, with the term "feudal serfdom" meaning largely being used by the People's Republic of China as a justification for their taking control of Tibet.