Treatise on Armament Technology, Volume 36

...so the siege could be broken. When Yuan Shang’s troops arrived, Shen Pei the general defending the city sent his own soldiers out to the north of the city to join the attack. Cao Cao intercepted and struck them; they were defeated and retreated. Yuan Shang fled toward Zhongshan. Cao Cao then executed Shen Pei. He went to the tomb of his old rival, Yuan Shao, where he wept and offered sacrifices. He comforted Yuan Shao’s wife, restored the family's personal property, and granted them silk, cotton, and grain from the public stores.

Previously, when Yuan Shao and Cao Cao first raised their righteous armies together, Yuan Shao asked Cao Cao, "If we champion this cause but things do not go well, what region could we rely upon as a base?"

Cao Cao replied, "What is your own opinion, my friend?"

Yuan Shao said, "To the south, I would hold the lands north of the Yellow River Hebei, protected by the mountains of Yan and Dai regions in the far north near the modern border of Shanxi and Hebei. I would incorporate the multitudes of the northern and western tribes original: "Rong" and "Di" and then look southward to contend for the empire. Perhaps in this way, I could succeed."

The main point of the argument Cao Cao replied, "I shall employ the wisdom and strength of all people under heaven, guiding them with the Way the Dao, or the principles of right governance. If I do this, there is nothing that cannot be achieved."

In the ninth month, [the Emperor] appointed Cao Cao as the Governor of Ji Province the wealthy region he had just conquered. Cao Cao resigned his post in Yan Province. He summoned the scholar Cui Yan to serve as an Aide-de-Camp and said to him, "Yesterday, when I examined the census records, I found we can raise three hundred thousand men. Truly, this is a great province."

Cui Yan replied, "Today, the Nine Provinces a traditional name for all of China are fractured and torn apart. The two Yuan brothers have turned weapons against one another..."