After Battle of Red Cliffs, the principal external contradiction of Liu Bei changed fundamentally, and the first task was to prevent it from being annexed by Sun Quan. This left Jiangdong with a powerful opponent and became the best way to contain Sun Quan.
I don't want to make enemies with Cao Shi, and I don't want to cause more wars. When Cao Cao was killed, future generations would inevitably seek revenge from Liu Bei. Although Cao Cao was defeated, he made further progress and died without being stiff. Liu Bei's penny is no match for Cao Cao's, and Sun Quan will definitely sit still and watch the tiger fight, and the fisherman will benefit. Moreover, killing Cao Cao will lead to a greater war in the northern group, and there will be no more military talents like Cao Cao. Xiliang Marten and Han Sui will also take advantage of the situation, and the situation will get out of control. Liu Bei can no longer unify the world.
Take good care of Guan Yu. Since his visit to Caotang, Zhang Fei has been very critical of Zhuge Liang, especially for 5. He didn't listen to Zhuge Liang, and often didn't listen to his instructions. If Liu Bei is absent, it is impossible to mobilize him. Knowing that Cao Cao would take Huarong Road, and Guan Yu was too loyal to kill Cao Cao, Kong Ming released Cao Cao and returned the favor. To this end, I was persuaded by the military order, and later by Kong Ming. This can also be interpreted as: it was not Liu Bei who let Cao go, but he let Cao go privately, talking about the loyalty and righteousness of China people.
Let Cao Cao go, and you can better share the fruits of victory. If Cao Cao is killed, there will be chaos in the north and it will be impossible to go south. Sun Quan must take the opportunity to destroy Liu Bei or drive him away. Longzhong can't talk about the three pillars mentioned. It is even more impossible for Liu Bei to take the opportunity to occupy Jingzhou. Even if he does, he will be recaptured by Sun Quan. Taking Cao Cao as a strong enemy, Liu Bei could bargain with him, so Liu Bei borrowed Jingzhou. Later, Yizhou was captured, and finally formed a situation of tripartite confrontation among the three countries. I think all this is because Zhuge Liang didn't kill Cao Cao.
Zhuge Liang is far-sighted, and Huarong Road is wise not to kill Cao Cao. Because of his outstanding political foresight and unparalleled talent, he finally contributed to the tripartite confrontation among the three countries. What do you think of Zhuge Liang?