Cao Cao then ordered Xun You and Cao Hong to remain behind to guard his main camp, while he personally led his forces to attack Wuchao and succeeded in destroying Yuan Shao's supplies and killed Chunyu Qiong in battle. As the tide turned against Yuan Shao, two of his generals, Zhang He and Gao Lan (), destroyed their own camps and led their men to defect and surrender to Cao Cao's side. When Zhang He and Gao Lan showed up at Cao Cao's main camp, Cao Hong felt suspicious and was reluctant to accept their surrender. Xun You told Cao Hong, "Zhang He was angry that Yuan Shao did not listen to him so he decided to defect. Sir, what's there to suspect about him?" Cao Hong then accepted their surrender. After Yuan Shao's death in June 202, Cao Cao launched a campaign against Yuan's sons Yuan Tan and Yuan Shang and defeated them at the Battle of Liyang. In the following year, when Cao Cao was planning to attack Liu Biao, he received news that Yuan Tan and Yuan Shang had started fighting over control of Ji Province. Yuan Tan sent his adviser Xin Pi to convey to Cao Cao his wish to surrender and seek aid from Cao in countering his brother. Cao Cao considered accepting Yuan Tan's surrender and sending troops to aid him, and then consulted his advisers. Most of them thought that Liu Biao was more powerful and that Yuan Tan and Yuan Shang posed no threat, so they urged Cao Cao to attack Liu Biao first. Xun You had a different opinion from them. He said, "The Empire has experienced so much turmoil, yet Liu Biao has holed up in the Jiang and Han regions. This shows that he has no intention of expanding his territory. The Yuans occupy four provinces and have 100,000 troops. Yuan Shao had treated his subordinates generously and hoped that his sons would cooperate harmoniously to safeguard his territories; that was why turmoil in the Empire never seemed to end. As of now, relations between the brothers have deteriorated and they seek to destroy each other. If one of them defeats and absorbs the other, he will become more powerful and more difficult to defeat. If you take advantage of their internal conflict to defeat them, you will restore stability in the Empire. You shouldn't miss this great opportunity." Cao Cao agreed, accepted Yuan Tan's surrender and led his forces to attack Yuan Shang. Yuan Tan later rebelled against Cao Cao but was defeated and killed at the Battle of Nanpi in 205.