In the current LAC standoff between India & China all kinds of theories have been given in the Indian press from a COVID-19 angle to a desire in Beijing to teach India a lesson for getting too close to the west.
However, a fundamental Chinese motivation has been ignored.
Ironically a Tibetan empire in constant conflict with its arch-enemy in Imperial China & China’s greatest threat on its western flank.
Both countries also had regional allies with China frequently allying with the Arab Caliphate on Tibet’s Western flank to pressure it.
It also exercised suzerainty.
Then came a collapse due to internal power struggles & assassination of its last King.
One of them was Ladakh established by Nyima-Gon or descendant of a Royal Tibetan Family lineage.
Such links to the Imperial past strengthened claims of the new Kings.
Then as the Mongols rose under Ghengis in the 13th Century much of Asia was put under Mongol rule or suzerainty.
However, Tibet was administered separately by Mongols who granted a certain autonomy & appointed Tibetan Sakya sect head as head of Tibet.
Political clout lay with Mongols though.
The 17th century saw the rise of the Gelugpa sect or Dalai Lama aided by Khoshut Mongols but this was still largely a local show.
China’s new Manchu Dynasty expanded Imperial China to its greatest territorial extent ever from the 18th to 20th century.
From then on the Qing became an important player in Tibet though Tibet was still governed by the Dalai Lamas.
The Qing control though varied on events and it’s influence waned ending in 1911.
To complicate the matter the Qing period of influence in Tibet was when India was under the British who was exploring the frontiers with Tibet.
Jammu and Kashmir in turn was effectively under British suzerainty who exercised power over the Sikhs and Dogras.
Tibet then rejected the MacMohan line.
In 1921 the British ignore the Convention with Russia and stressed Shimla convention & the MacMohan line.
China now claims AP as Southern Tibet.
But, Nehru was outraged with the invasion & so secured what india got from British & it’s frontiers.
The difference from Qing era was suzerainty changing into territory consolidation.
This led to 1962 Sino-Indian war.
This was a major change in the Indian position on Tibet.
India’s new position was now a complete acceptance of China’s position over Tibet and all its territories with no recognition of even the 1950 invasion.
But PRC modern approach is a complete amalgamation and sinicization.
So for the PRC/CCP view it feels it has given up on a lot of Imperial Tibet/Old Tibet territory claims and cannot backdown now.