Gongsun Zan
In 198, Yuan Shao advanced against Gongsun Zan and encircled his remaining force at Yijing (present-day Xiong County, Hebei). By early 199, Yuan Shao had completely defeated Gongsun Zan at the Battle of Yijing and held absolute power over the four provinces north of the Yellow River. Then, after establishing an alliance with the Wuhuan tribes on the northern frontier, Yuan Shao turned his attention to Cao Cao, who had consolidated his own power base to the south of the Yellow River.