Emperor Taizong of Tang (r. 626-649), the second emperor of the Chinese Tang Dynasty, faces a major threat from Tang's northern neighbor, the Eastern Turkic Khaganate, who had subjugated his father Emperor Gaozu of Tang in several ways.

Early in Emperor Taizong's reign, he had placated the Eastern Turkic Khaganate's Jiali Khan Ashina Duobi, but, preparing for several years for a major offensive against the Eastern Turkic Khaganate (including forming an alliance with the Eastern Turkic Khaganate's restless vassal Xueyantuo, which is ready to throw off the Eastern Turkic yoke), he launches it in winter 629, with the major general Li Jing in command, and in 630, after Li Jing captures Ashina Duobi, the Eastern Turkic Khaganate is destroyed.

After the destruction of the Eastern Turkic Khaganate, the control of the territory north of Tang largely falls to Xueyantuo, and Emperor Taizong initially tries to settle a large number of the Eastern Turkic people within Tang borders.

Eventually, after an incident where he is nearly assassinated by a member of the Eastern Turkic royal house, Ashina Jiesheshuai, he tries to resettle the Eastern Turkic people north of the Great Wall and south of the Gobi Desert, to serve as a buffer between Tang and Xueyantuo, creating a loyal Eastern Turkic Khaganate's prince Ashina Simo as the Qilibi Khan, but Ashina Simo's reign collapses around the new year of 645 due to dissent within and pressure from Xueyantuo without, and Tang will not attempt to recreate the Eastern Turkic Khaganate any further (although there are remnant tribes that will later rise-- and the Eastern Turkic Khaganate is, during the reign of Emperor Taizong's son Emperor Gaozong, reestablished under Ashina Gudulu, as a hostile power against Tang).