In 215, after Cao Cao destroyed Zhang Lu in Hanzhong, due to his old age (61 years old), his confidence in unifying the world was shaken, believing that it was impossible to destroy Liu Bei and Sun Quan. Therefore, since then, he himself no longer personally led the expedition, but focused his work mainly on internal affairs, that is, preparing for the usurpation of the Han Dynasty as emperor. As for the military side, Cao Cao divided the southern part of his territory into three defensive areas, and mainly defended Liu Bei and Sun Quan, no longer expecting to eliminate them.
Cao Cao once entered the temple to see Emperor Xian, and Emperor Xian of Han said to Cao Cao, "If you can assist me, be more lenient; otherwise, you will leave me behind." Cao Cao was stunned and hurriedly responded to the request for resignation. The old system of the Han Dynasty stipulated that when the three dukes who led the troops met the emperor, they were all held hostage by tiger warriors with swords. After Cao Cao left the palace, he looked back and sweated, and never saw Emperor Xian again. According to the historical records: "The Han Dynasty physician Ling Jiping conspired with Geng Ji and Si Zhi Wei Huang of Shaofu to rebel, secretly attacked Xu Du, and burned the barracks of Shi Wangbi, the chancellor of the chancellor. In other words, the Ji Pingren contacted more than a thousand people in Xuchang and attacked Cao Cao's highest military and political commander who remained in Xuchang. The point is that he almost killed Cao Cao's top military and political commander who remained in Xuchang.
At the time of the Battle of Hanzhong, Liu Bei's clique was at the peak of its military strength, coupled with the two places of Yizhou and Jingzhou in its hands, and sun Wu in the east, occupying the favorable time and place. And Cao Cao's side? First, Xiahou Yuan died in battle at Dingjun Mountain, and morale was greatly damaged, and then the grain and grass were robbed, and his back was cold. The impact on both sides can also be seen. If we want to see why Cao Cao eventually failed miserably, we still need to look back at the war process at that time to have a more objective summary.
When Cao Cao retreated, he moved most of the people of Hanzhong to Guanzhong, and it can be said that Cao Cao planned to abandon Hanzhong at the beginning and move the people of Hanzhong from the beginning. Cao Jun and the Shu army attacked and defended for two years, but only provided time and space for Cao Cao to move away the people. At that time, Guan Yu of Jingzhou was launching the Battle of Xiangfan, and Sun Quan was also eyeing Cao Wei, if Cao Cao fought in Hanzhong for a long time, then the Central Plains were in danger! In comparison, the Central Plains were more important to Cao Cao. Cao Cao believed that as long as there were people, it was only a matter of time before Hanzhong was taken, there was no need to compete with Liu Bei for the long and short, and he cared about the gains and losses of one city and one place, so he moved the people and left the land to Liu Bei.