At the same time, Emperor Taiwu also ordered that Juqu Mujian's mother be honored as the Princess Dowager of Hexi.
Juqu Mujian was forced to divorce Princess Li, who was exiled to Jiuquan from the Northern Liang capital Guzang (姑臧, in modern Wuwei, Gansu), and died soon thereafter.
(Despite the marriage, Emperor Taiwu considered launching a campaign against Northern Liang, but at the urging of Li Shun (李順), who had previously advocated military action as well but by this point was against such actions, arguing that the army was still tired from conquering Northern Yan and Xia as well as fighting Liu Song and needed rest, Emperor Taiwu postponed the plans.)
Emperor Taiwu sent doctors, who were able to save Princess Wuwei's life, and he then demanded that Juqu Mujian turn over Lady Li.
At the encouragement of the prime minister Cui Hao, Emperor Taiwu again prepared military action.
With Yuan He, the son of Southern Liang's last prince Tufa Rutan, as guide, he launched a speedy attack and arrived at Guzang quickly.
Juqu Mujian, in shock, refused to surrender, defending the city against a siege, while seeking immediate military assistance from Rouran's Chilian Khan, Yujiulü Wuti.
Yujiulü Wuti did launch a surprise attack on Pingcheng to try to force Emperor Taiwu to give up the campaign, but after initial successes, he failed to capture Pingcheng, and his brother Yujiulü Qiliegui (郁久閭乞列歸) was captured by Northern Wei forces.
In 447, however, accusations were made that when Juqu Mujian opened up the royal treasury when Guzang fell, that the treasures ended up back in his possession.