<P> Civil war in China was almost totally diminished by 626, along with the defeat in 628 of the Ordos Chinese warlord Liang Shidu; after these internal conflicts, the Tang began an offensive against the Turks . In the year 630, Tang armies captured areas of the Ordos Desert, modern - day Inner Mongolia province, and southern Mongolia from the Turks . </P> <P> After this military victory, Emperor Taizong won the title of Great Khan amongst the various Turks in the region who pledged their allegiance to him and the Chinese empire (with several thousand Turks traveling into China to live at Chang'an). On June 11, 631, Emperor Taizong also sent envoys to the Xueyantuo bearing gold and silk in order to persuade the release of enslaved Chinese prisoners who were captured during the transition from Sui to Tang from the northern frontier; this embassy succeeded in freeing 80,000 Chinese men and women who were then returned to China . </P> <P> While the Turks were settled in the Ordos region (former territory of the Xiongnu), the Tang government took on the military policy of dominating the central steppe . Like the earlier Han Dynasty, the Tang Dynasty, along with Turkic allies like the Uyghurs, conquered and subdued Central Asia during the 640s and 650s . During Emperor Taizong's reign alone, large campaigns were launched against not only the Göktürks, but also separate campaigns against the Tuyuhun, and the Xueyantuo . Taizong also launched campaigns against the oasis states of the Tarim Basin, beginning with the annexation of Gaochang in 640 . The nearby kingdom of Karasahr was captured by the Tang in 644 and the kingdom of Kucha was conquered in 649 . </P> <P> The expansion into Central Asia continued under Taizong's successor, Emperor Gaozong, who invaded the Western Turks ruled by the qaghan Ashina Helu in 657 with an army led by Su Dingfang . Ashina was defeated and the khaganate was absorbed into the Tang empire . The territory was administered through the Anxi Protectorate and the Four Garrisons of Anxi . Tang hegemony beyond the Pamir Mountains in modern Tajikistan and Afghanistan ended with revolts by the Turks, but the Tang retained a military presence in Xinjiang . These holdings were later invaded by the Tibetan Empire to the south in 670 . For the remainder of the Tang Dynasty, the Tarim Basin alternated between Tang and Tibetan rule as they competed for control of Central Asia . </P>

Who conquered central asia from mongolia to the caspian sea