regions. In 437, the marriage negotiations that Emperor Taiwu had with Liu Song's Emperor Wen appeared to reach some fruition, as Emperor Wen sent his official Liu Xibo (劉熙伯) to Northern Wei to discuss details of how one of his daughters would be married into the Northern Wei imperial household, but at this time, Emperor Wen's daughter died, and the negotiations ended. Also in 437, exasperated by the rampant corruption that his local officials were engaging in (which was somewhat necessary for them because at this point, no Northern Wei officials received a salary), he issued an edict creating incentives for low-level officials and commoners to report officials for corruption. However, the edict did not have its calculated effect, as the people who had evidence of the officials' corruption instead used the knowledge to blackmail the officials, and the officials continued to be corrupt. Later in 437, Emperor Taiwu married his sister Princess Wuwei to Juqu Mujian, and Juqu Mujian sent his heir apparent Juqu Fengtan (沮渠封壇) to Pingcheng to be a hostage. Despite this, he continued to consider conquering Northern Liang, but at Li Shun's urging, delayed it. In 438, Emperor Taiwu launched a major attack on Rouran, but Rouran forces largely eluded his, and he made little gain. In 439, aggravated that Juqu Mujian's sister and sister-in-law Lady Li (with whom Juqu Mujian was having an affair) had tried to poison Princess Wuwei, and also unhappy that Juqu Mujian had friendly relations with Rouran, decided to launch a major attack on Northern Liang. Li Shun, who had previously advised him to attack Northern Liang, by this point had somehow switched positions and, along with Tuxi Bi, opposed such military actions, stating falsely that there was so little water and grass for grazing in Northern Liang that Northern Wei troops would suffer from thirst and hunger. At Cui Hao's insistence, however, Emperor Taiwu believed that he could conquer Northern Liang, and he launched the campaign. He quickly reached the Northern Liang capital Guzang (姑臧, in modern Wuwei, Gansu) in the fall, capturing it after a short siege. Meanwhile, Yujiulü Wuti had launched a surprise attack on Pingcheng to try to save Northern Liang, but was repelled. (Cui Hao, who was a political enemy of Li Shun's, would attribute Li's switch in position to bribes by Juqu Mujian, and later Emperor Taiwu would force Li to commit suicide.) Northern Liang