Xue Rengui
The Tuyuhun government was split between the pro-Tang and pro-Tibet factions, with the latter increasingly becoming stronger and collaborated with Tibet to bring about an invasion. The Tang sent general Xue Rengui to lead 100,000 troops to fight Tibet in Dafeichuan (present Gonghe County, Qinghai). They were annihilated by the ambush of 200,000 troops led by Dayan and the Tibetans. The Tibetan Empire took over the entire territory of the Tuyuhun.