Su Dingfang
The conquest of the Western Turks, known as the Western Tujue in Chinese sources, was a military campaign in 655–657 led by the Tang Dynasty generals Su Dingfang and Cheng Zhijie against the Western Turkic Khaganate ruled by Ashina Helu. The Tang campaigns against the Western Turks began in 640 with the annexation of the Tarim Basin oasis state Gaochang, an ally of the Western Turks. Several of the oasis states had once been vassals of the Tang Dynasty, but switched their allegiance to the Western Turks when they grew suspicious of the military ambitions of the Tang. Tang expansion into Central Asia continued with the conquest of Karasahr in 644 and Kucha in 648. Cheng Zhijie commanded the first foray against the West Tujue, and in 657 Su Dingfang commanded the main army dispatched against the Western Turks, while the Turkic generals Ashina Mishe and Ashina Buzhen led the side divisions. The Tang troops were reinforced by cavalry supplied by the Uyghurs, a tribe that had been allied with the Tang since their support for the Uyghur revolt against the Xueyantuo. Su Dingfang's army defeated Helu at the battle of Irtysh River.