The Tang destroy the Eastern Turkic Khaganate: Taizong becomes “Heavenly Khagan”

In 626, shortly after Taizong came to the throne, Illig Qaghan and his nephew Tuli had ridden to the Wei River bridge outside Chang’an and withdrawn only after the emperor came out to parley and made peace. Within a few years their power was crumbling: heavy snows killed the herds, the Tiele tribes north of the Gobi rose under the Xueyantuo and the Uyghurs, and Tuli, who had quarrelled with his uncle, went over to the Tang. On 13 December 629 — in the eleventh month of the third year of Zhenguan — Taizong sent his generals, among them Li Shiji, Chai Shao and Xue Wanche, by several routes, more than 100,000 men in all, under the overall command of Li Jing.

In the first month of 630 Li Jing advanced from Mayi with 3,000 picked horsemen and took Dingxiang in a night attack, while Li Shiji defeated the Turks at Baidao. Illig fell back to the Iron Mountain (Tieshan) beyond the Yin Mountains and offered to submit, and Taizong sent the envoy Tang Jian to him. Li Jing, suspecting that the khagan was playing for time until the grass grew and he could slip away north of the Gobi, attacked without regard for the envoy: on 27 March 630 his vanguard of 200 horsemen under Su Dingfang came up through the fog to within seven li of the khagan’s tent before being noticed. The Turks scattered; by the account of the Zizhi tongjian more than 10,000 were killed and over 100,000 people captured, the khagan’s wife, the Sui princess Yicheng, was killed, and Li Shiji, blocking the road across the desert, took more than 50,000 others. Illig fled to Sunishe, a chief who had stayed loyal to him; pressed by the Tang general Li Daozong, Sunishe seized him, and on 2 May Zhang Baoxiang took the khagan from his camp and sent him to Chang’an.

That spring — before Illig’s capture according to the Zizhi tongjian, after it according to the Old Book of Tang — the chiefs of the steppe peoples came to court and asked Taizong to take the title Tian Kehan, “Heavenly Khagan”, and his letters to the rulers of the north-west afterwards bore it. In May Illig was brought before the emperor, who listed his crimes but spared his life; he died in Chang’an in 634. The Eastern Turkic Khaganate ceased to exist: some of its tribes went over to the Xueyantuo, others fled west, and about 100,000 people who surrendered were settled along the frontier from Youzhou to Lingzhou under their own chiefs, who received Tang ranks — the plan of Wen Yanbo, adopted against Wei Zheng’s advice to send them back beyond the frontier. Half a century later, in 682, Qutlugh of the Ashina house revived the khaganate.