Emperor Taizong's Campaign Against Xiyu States - Background

Background

In contrast to its eastern cousin Eastern Turkic Khaganate, Western Turkic Khaganate did not pose a major threat to Tang Dynasty in the early years of Tang's existence, as it was farther from Tang territory and not attacking Tang. Moreover, Western Turkic Khaganate constantly suffered from internal divisions and was unable to concentrate itself against Tang. Its hegemony over the Western Regions was therefore unchallenged by Tang. In turn, both the Western Turkic Khaganate itself and its vassal-allies in the region at times nominally submitted to Tang overlordship. For example, in 619, just briefly after Emperor Gaozu established Tang in 618 and was still battling for supremacy with China with a number of rival rulers, both Western Turkic Khaganate's Tongyehu Khan Ashina Tong and Gaochang's king Qu Boya submitted tributes to him. In 625, in fact, Ashina Tong sought marriage with a Tang princess, and Emperor Gaozu initially agreed, but Eastern Turkic Khaganate's Illig Qaghan Ashina Duobi was displeased about the potential of a Tang-Western Turkic alliance and threatened Ashina Tong against it, and the marriage was never carried out.

In 626, Emperor Gaozu's son Li Shimin the Prince of Qin, who had been in an intense rivalry with his older brother Li Jiancheng the Crown Prince, ambushed and killed Li Jiancheng and another brother who supported LI Jiancheng, Li Yuanji the Prince of Qi, at Xuanwu Gate. He then effectively forced Emperor Gaozu to first create him crown prince and then pass the throne to him (as Emperor Taizong). After Emperor Taizong took the throne, in 628, Ashina Tong was killed by his uncle, Ashina Moheduo, who seized the throne (as Qulipiqie Khan). However, some of the people supported Ashina Tong's son Ashina Dieli as khan (as Siyehu Khan). Both sought aid and marriage from Tang, and Emperor Taizong declined both. (Eventually, in 630, Ashina Dieli was able to defeat and kill Ashina Moheduo, again reuniting the Western Turkic Khaganate.) Meanwhile, Gaochang's king Qu Wentai (Qu Boya's son and successor) made a visit to the Tang capital in Chang'an in 630-631, and was welcomed in grand ceremonies.

In 632, Ashina Dieli, who had lost the support of his people due to his cruelty and suspicions, failed in an attack against Xueyantuo, and after the failure, his own substituent tribes Shebeidaguan (設卑達官) and Nushibi (弩失畢) attacked him and forced him to flee to Kangju, and he soon died in exile. The people supported his cousin Ashina Nishu as Duolu Khan, and Ashina Nishu nominally submitted to Tang and received Tang titles. The situation continued after he died in 634 and was succeeded by his brother Ashina Tong'e (as Dielishi Khan).

Also in 632, there would be an incident that would contribute to the chilling of relations between Tang and Gaochang. Yanqi had previously been directly having contact with China through a road through the desert, which later was closed, forcing Yanqi emissaries to go through Gaochang, apparently aiding the Gaochang economy in doing so. In 632, Yanqi's king Long Tuqizhi requested that the desert road be reopened, and Emperor Taizong approved of the request, leading to Gaochang resentment, and Gaochang attacked Yanqi, withdrawing only after pillaging.

By 638, it was said that Ashina Tong'e had lost the hearts of the people, and the northern half of the khanate supported an Eastern Turkic prince, Ashina Yugu as Yipiduolu Khan. There were major battles between Ashina Tong'e and Ashina Yugu, but neither side was able to prevail, and therefore divided the khanate in two, with Ili River serving as their boundary. The division continued after Ashina Tong'e died in 639 and was succeeded by his nephew Ashina Bobu (as Shaboluoyehu Khan).