Emperor Taizong of Tang (r. 626-649), the second emperor of Chinese dynasty Tang Dynasty, subjugated the Xianbei state Tuyuhun in 635. Thereafter, Tuyuhun's southwestern neighbor, the Tibetan state Tufan, rose in power and soon displaced Tuyuhun as the major threat to Tang's west. In 638, in retaliation to Emperor Taizong's refusal to give him a Tang princess in marriage, Tufan's Songtsän Gampo, believing that the refusal was due to Tuyuhun interference, attacked Tuyuhun and Tang with a grand force of 200,000, and while Tang's 50,000 forces, commanded by Niu Jinda (牛進達), serving under Hou Junji, repelled the Tufan attack, Emperor Taizong decided to placate Songtsän Gampo by giving him a distant niece, Princess Wencheng, in marriage. For the rest of Emperor Taizong's reign, there would be n