Battle of Guandu
In early 201, after Cao Cao defeated his northern rival Yuan Shao at the Battle of Guandu, he first sent Zhang Liao to pacify the various counties in Lu State (魯國; around present-day Qufu, Shandong), and then ordered him and Xiahou Yuan to lead an army to attack a minor warlord Chang Xi (昌豨) in Donghai Commandery (東海郡; around present-day Linyi, Shandong). Zhang Liao and Xiahou Yuan had besieged Chang Xi for months but were unable to defeat him and their supplies were running out, so they considered retreating.