Conquest Of The Tarim Basin
Songtsen Gampo was succeeded by his grandson Mangsong Mangtsen, who began his reign by conquering the ‘A zha (aka “the Tuyuhun”) from Mongolia, a people who had gone to war against both the Chinese Tang dynasty and the Tibetans. The defeat of the ‘A zha forced their king, Nuohebo, to flee to China for refuge with his remaining troops where they were resettled to keep them under China’s thumb.
Mangsong was then able to expand Tibetan influence into Chinese territory, a feat his grandfather had never accomplished. Mangsong also extended Tibetan power into the Tarim Basin in modern Xinjiang as far as the Wakhan Valley in what is now Afghanistan.
The Tang were not pleased about losing control of the oasis cities of the Silk Road, which were vital for both trade and communication in western China. However, the Tibetans were able to subjugate the Western Turks of the region and gain their fealty by 670, thereby controlling large trade centers such as Kashgar and Khotan.
The Tang sent a large and formidable army to challenge the Tibetan expansion. But the Chinese were decisively defeated by a massive Tibetan force led by General mGar Khri ‘bring at Dafeichuan, which forced the Chinese to withdraw. During this period, the mGar clan (aka the “Gar clan”) was the real power behind the throne of Tibet, as chief minister Gar Songtsan had taken over much of the king’s authority. The mGar had become a threat to royal power that had to be eliminated.