In 625, Ashina Tong sought marriage with a Tang princess, and Emperor Gaozu initially agreed, but the Eastern Turkic Khaganate's Illig Qaghan Ashina Duobi was displeased about the potential of a Tang-Western Turkic alliance and warned Ashina Tong against it, ensuring that the marriage never took place. 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 Li Yuanji, the Prince of Qi, at Xuanwu Gate. He then forced Emperor Gaozu to first enfeoff him as crown prince and then abdicate the throne, leaving it open for Li Shimin to take the throne as Emperor Taizong. After Taizong ascended to power in 628, Ashina Tong was killed by his uncle, Ashina Moheduo, who seized the throne as Qulipiqie Khan. However, some key Turks supported Ashina Tong's son Ashina Dieli as khan. Both sought aid and marriages from Tang China, 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 made a visit to Chang'an in 630, and was received warmly by the Tang court. In 632, Ashina Dieli, who had lost the support of his people due to his cruel rule, lost a campaign against the Khazars, which caused the tribes Shebeidaguan () and Nushibi who had formerly supported him to rebel and force him to flee to Kangju. Bereft of a leader, the Turks chose Ashina Nishu as Duolu Khan, and Ashina Nishu nominally submitted to the Tang dynasty and received Tang titles. The enmity continued, however, even after Nishu died and was succeeded by his brother, Ashina Tong'e. 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 the Ili River serving as their boundary.