In the first year of Jian 'an, Cao Cao carried Han to Xuchang, and from then on, he began to "carry the emperor to make the princes". Later, Yuan Shu and Lu Bu were destroyed one after another, and their sphere of influence expanded. Cao Cao controlled most areas south of the Yellow River, north of Huaihe River and north of Hanshui River, and confronted Yuan Shao in the lower reaches of the Yellow River. It is said that Yuan Shao is far more powerful than Cao Cao.

In January of the fifth year of Jian 'an, Yuan Shao organized 100,000 troops to go south, while Cao Cao "had less than 10,000 soldiers". The two sides fought in Guandu, and Cao Cao won more with less. Since then, Cao Yuan's strength has changed greatly, and northern China has moved from division to unification.

But did Cao Cao really defeat Yuan Shao's 100,000 troops with so few soldiers? Were the forces of Yuan and Cao really so different in the battle of Guandu? In fact, this is a debatable question. In the battle of Guandu, Cao Cao took an arc defensive front. He sent Qingzhou to occupy Qi, Beihai, Yong 'an and other places, and sent Cheng Yu to guard Juancheng to prevent Yuan Shao from attacking Xuchang from the east. Wei Ji sent people to guard the Guanzhong; Zhong Wei was sent to guard Hanoi; Send Coss to catch and shoot dogs; Then he sent Yu Jin and Liu Yantun to Yanjin and Baima to meet them. In September, Cao Cao returned to Xu and deployed some troops to guard Guandu. Imagine such a long front. What would Cao do if there were less than ten thousand soldiers in Cao Can?

According to the chronicle, in August of the fifth year of Jian 'an,' before the joint venture, sand was a chariot, and it was dozens of miles from east to west. It is not good to go to war. When there were less than ten thousand soldiers, twelve or thirteen people were injured. Shao re-entered Lin Guandu and started from Tushan Tunnel. It is also done in public, so as to correspond. "Even dozens of battalions, how can thousands of troops do it? Most battles that win more with less are won with faster, because if the fighting time is prolonged, it will be very unfavorable to the party with insufficient troops. The battle of Guandu lasted for eight or nine months. If you can resist for such a long time, even if Cao Cao is defeated.