Yuan Xi
Cao Cao's victory at the Battle of Guandu was a decisive one and marked the turn of the tide in his struggle for power with Yuan Shao. Yuan Shao died two years later and his youngest son Yuan Shang was made his successor. His oldest son Yuan Tan was furious with the succession and fought with his younger brother. This resulted in internal conflict within Yuan Shao's forces. Yuan Shao's pool of talented advisors and generals were also divided into two factions by the conflict – one supported Yuan Shang and the other supported Yuan Tan. Cao Cao seized the opportunity to launch an attack on Yuan Tan's base at Liyang. Though Cao Cao eventually withdrew, Yuan Tan came to resent Yuan Shang even more during course of the battle, which led to open warfare between the brothers. Yuan Tan eventually allied with to Cao Cao against Yuan Shang, but Cao Cao accused him of violating some terms of the alliance and killed him in battle. On the other hand, Yuan Shang suffered defeats at the hands of Cao Cao and fled north to join his second brother Yuan Xi. Cao Cao's forces pursued them and defeated the Wuhuan tribe, the Yuan brothers' ally, in the Battle of White Wolf Mountain. Yuan Shang and Yuan Xi fled to Liaodong to seek shelter under the warlord Gongsun Kang in 207, but Gongsun killed them instead and sent their heads to Cao Cao. By then, most of northern China was unified under Cao Cao's control, and Cao Cao could begin to turn his attention to the south.