松赞干布
In fall 638, Tibet's Songtsän Gampo, displeased that Emperor Taizong had declined to give him a Tang princess in marriage and believing that Murong Nuohebo had persuaded Emperor Taizong to decline the marriage proposal, launched a major attack with forces of 200,000 on Tuyuhun and then on several Tang prefectures, putting Song Prefecture (, roughly modern Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan) under siege. Emperor Taizong commissioned Hou Junji, assisted by Zhishi Sili (), Niu Jinda (), and Liu Jian (), of a total of force of 50,000 to counterattack, and Niu, who commanded the forward forces, defeated Tibetan forces at Song Prefecture. Songsän Gampo withdrew and sued for peace, but still sought to marry a Tang princess. Emperor Taizong agreed this time.