Juqu Mujian
In 439, Juqu Mujian was entangled in a scandal that adversely affected his relationship with Northern Wei. He and his two brothers were all having affairs with the wife of another brother, Lady Li, and Lady Li then plotted, with a sister of Juqu Mujian, to poison Princess Wuwei. Emperor Taiwu sent doctors, who were able to save Princess Wuwei's life, and he then demanded that Juqu Mujian turn over Lady Li. Juqu Mujian refused, and only sent Lady Li to Jiuquan. Meanwhile, the Northern Wei messengers to the Xiyu kingdoms, who were going through Northern Liang frequently, were alleging that Juqu Mujian had informed Xiyu kingdoms that they should not submit to Northern Wei and should submit to Rouran instead. 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. After nearly two months of siege, Juqu Mujian's nephew Juqu Wannian (沮渠萬年) surrendered to Northern Wei forces, and Guzang collapsed. Juqu Mujian tied his own arms as sign of submission and surrendered. Emperor Taiwu took the city, but continued to treat Juqu Mujian with respect, as a brother-in-law, and while he took Juqu Mujian to Pingcheng, he continued to allow him to carry the title of Prince of Hexi. (Allegedly, as he surrendered, he opened up the royal treasury to let it be pillaged—an action that would have detrimental consequences to him later on.)