Cao Cao scored a decisive victory over
Yuan Shao at the
Battle of Guandu in 200. Yuan Shao died two years after his defeat and his sons
Yuan Tan and
Yuan Shang started fighting each other for control over their father's vast domain. Cao Cao defeated Yuan Tan and Yuan Shang at the
Battle of Liyang in 202–203 and won several consecutive battles. At the time, many of Cao Cao's generals urged Cao to take advantage of his successes to continue attacking the Yuans, but Guo Jia said, "Yuan Shao loved both sons so he couldn't decide between them who would succeed him. With advisers like
Guo Tu and
Pang Ji to assist the Yuans, internal conflict will definitely break out between them. If we press on our attacks, the Yuans will unite to resist us. If we withdraw our forces, the Yuans will start fighting among themselves. Why don't we turn south and attack
Liu Biao in
Jing Province first? We should wait until the Yuan brothers start fighting each other and then attack them. We'll achieve victory in this way." Cao Cao agreed and prepared for a campaign against Liu Biao. Internal conflict did break out between Yuan Tan and Yuan Shang later, which resulted in Yuan Tan being defeated by his younger brother. Yuan Tan retreated to Pingyuan () and sent
Xin Pi to meet Cao Cao, agreeing to surrender to Cao and requesting for assistance in dealing with Yuan Shang. Cao Cao led his forces north and defeated Yuan Shang at the
Battle of Ye in 204. In 205, Cao Cao attacked Yuan Tan on some pretence and defeated him at the
Battle of Nanpi. By then, Cao Cao had pacified most of
Ji Province in northern China. In recognition of his contributions, the Han imperial court enfeoffed Guo Jia as the Marquis of Weiyang Village ().
Battle of White Wolf Mountain When Cao Cao was preparing for another campaign against Yuan Shang (who had fled to join his second brother
Yuan Xi and the
Wuhuan tribes), many of his followers were worried that Liu Biao might send
Liu Bei (who had become a vassal under Liu Biao) to attack Cao Cao's base, the imperial capital Xu (許; present-day
Xuchang,
Henan). However, Guo Jia said to Cao Cao, "Your military might may be very well known now, but the Wuhuan will definitely not set up defences because they are deluded by a false sense of security since they are far away from you. As such, if you seize this opportunity to launch a surprise attack on them, you can eliminate them. Besides, Yuan Shao treated the ethnic minorities well and the Yuan brothers are still alive. Now, the people of northern China submit to you because they fear your military might, and you've yet to pacify them through benevolent governance. If you abandon the campaign and head south instead, the Wuhuan and Yuan Shao's former followers might rally the support of the people in northern China, who are likely to respond to their call. When that happens, the attention of
Tadun (a Wuhuan chieftain) will be aroused and he may think of attacking you, and by then we would have lost
Qing and Ji provinces. Liu Biao is a person who does nothing but sit and talk. He also does not trust Liu Bei as the latter is more capable than him – if he entrusts Liu Bei with important responsibilities, he will be worried that the latter will no longer submit to him; if he gives Liu Bei trivial tasks to do, the latter will be reluctant to serve him. Even if you empty your territories to campaign far away, you have no worries." Cao Cao proceeded with his campaign against the Yuan brothers and the Wuhuan. When Cao Cao's forces arrived at Yi (), Guo Jia said, "A swift army is powerful. Now, as we've travelled a long distance, we have much heavy baggage so we cannot launch a swift attack. If the enemy learns of our approach, they will definitely prepare defences. Why don't we leave the heavy baggage behind and send our light forces to take a shortcut and launch a surprise attack?" Cao Cao led his army through a secret passage at Lulong Pass () and headed directly towards the Wuhuan chieftains' headquarters. The Wuhuan were shocked when they heard of Cao Cao's approach and they hastily assembled their army, but were defeated by Cao Cao at the
Battle of White Wolf Mountain. Tadun was killed in battle. The Yuan brothers fled to
Liaodong to join the warlord
Gongsun Kang, who captured and executed them and then sent their heads to Cao Cao. ==Death==