Historically most of the conflict over Kashmir has been with the Paki, not the Chinese. This is different. China seems to be seeking to strengthen tactical and strategic ties with Pakistan at Indias expense. China has the initiative and appears to be deliberate in pressing the advantage.
When India was getting independence and being partitioned, Kashmir has a Hindu maharajah leading a mostly Muslim population. The maharajah acceded to India, contrary to the wishes of the people.