These incursions continued after Emperor Taizong became emperor in 626—although they appeared to decrease in frequency, as the only incursions recorded in the Chinese chronicle Zizhi Tongjian were in 628, when Tuyuhun forces attacked Min Prefecture (岷州, roughly modern Dingxi, Gansu), and 632, when Tuyuhun forces attacked Lan Prefecture (蘭州, roughly modern Lanzhou, Gansu).
Emperor Taizong agreed, but ordered that the Prince of Zun personally arrive in Chang'an to marry the princess.
Meanwhile, Murong Fuyun also attacked Lan and Kuo (廓州, also in modern Haidong) Prefectures and detained the Tang emissary Zhao Dekai (趙德楷).
In fall 634, Emperor Taizong sent the generals Duan Zhixuan (段志玄) and Fan Xing (樊興) to attack Tuyuhun with Tang forces, supplemented by soldiers from the Qibi (契苾) and Dangxiang tribes.
Apparently immediately after he withdrew, Tuyuhun forces again attacked Liang Prefecture (涼州, roughly modern Wuwei, Gansu).
In the initial stage of the campaign, some Dangxiang and Qiang tribes, apparently fearing that they would be involved, rebelled against Tang and fled to join Tuyuhun.
Most of Li Jing's subordinates believed that it was dangerous to venture further without adequate grazing supplies and advised withdrawal, but Hou opposed the idea, pointing out that this was the opportunity to destroy Tuyuhun.
In 638, a counterattack by the Tang general Niu Jinda (牛進達), under Hou's command, defeated Tibetan forces at Song Prefecture.
Meanwhile, the Tang military commander Xi Junmai (席君買) made a surprise attack against the Prince of Xuan, killing him and his two brothers, allowing Murong Nuohebo to return, albeit with the Tuyuhun people highly alarmed.
Murong Nuohebo and Princess Honghua abandoned their territory and fled to Liang Prefecture with his remaining followers, largely ending the existence of Tuyuhun as a separate state, although the Tuyuhun people would not be formally adopted into the Tang governmental structure until 672, when Murong Nuohebo was given a prefect title in a newly created Anle Prefecture (安樂州, in modern Wuzhong, Ningxia).