The Battle of Guandu-Sequel І
The war against Dong Zhuo ended disgracefully, and Cao Cao decided to work alone. He built up his troops again and, advised by his coterie, arranged for the royal family to settle on his lands, thus obtaining an edge in the fight for legitimacy from the fact that he, rather than any of the other competing warlords, was with the emperor. As his power grew and expanded, he came into confrontation with the domain of Yuan Shao, who was already powerful and dominant in northern China. Tensions built up and soon developed into a big clash in Guandu. It was a deadly wrestle for dominance between Yuan Shao the giant and Cao Cao the rising hero. One would have to go, and the winner would take all.
In AD 200 Yuan Shao took an army of100,000 on an expedition to Xuchang, where Cao Cao had the emperor with him. Vanity about an apparent advantage led Yuan Shao into disheartening defeats, first in Baima (today's Huaxian County, Henan Province) and then in Yanjin (in today's Henan Province). Confident that he still outnumbered Cao Cao, he nevertheless had his troops cross the Yellow River to engage the enemy's main forces in Guandu (northeast of today's Zhongmu, Henan Province). Cao Cao was awaiting him there. A month passed without either of them gaining a decisive victory, until one of Yuan Shao's advisors, named Xu You, intercepted information that Cao Cao's troops had overextended their supply line.
Xu You suggested that Yuan Shao launch a surprise attack on Xuchang with a small unit, which could be maneuvered around Guandu. His advice was totally ignored by his commander, who believed he could easily crush Cao Cao's army. Before he could give further explanations, a courier from Yecheng, the base city, entered with a message accusing someone related to Xu You of wrongdoing. Shared blame by association placed Xu You on Yuan Shao's blacklist, and whatever else he said about the current campaign no longer mattered. Humiliated, Xu You deserted Yuan Shao's camp and surrendered to Cao Cao, an old friend of his.