Ashina Helu
Emperor Taizong died in 649. Subsequent to his death, a Western Turkic prince that he had supported, Shabolüe Khan Ashina Helu (阿史那賀魯), defeated and killed the Yipishekui Khan, taking over Western Turkic, but subsequently broke away from Tang and attacked Tang territory. Emperor Taizong's son and successor Emperor Gaozong launched two campaigns against Ashina Helu. The first, launched in 655 and commanded by Cheng Zhijie (程知節), ended in failure, as it was forced to withdraw when supplies ran out. The second, launched in 657 and commanded by Su Dingfang, was a thorough victory, as Tang forces captured Ashina Helu and put Western Turkic territory under the control of two Western Turkic princes submissive to Tang, the Xinxiwang Khan Ashina Mishe (阿史那彌射) and the Jiwangjue Khan Ashina Buzhen (阿史那步真), becoming the dominant power in the region.