After the Battle of Chibi, Cao Cao was defeated by Sun Liu's alliance, and the defeat at the Battle of Chibi also represented that Cao Cao had lost his qualification to dominate the world. It should be known that in the Battle of Chibi, Cao Cao suffered heavy losses, so that Cao Cao lost his troops. Such a loss was something that Cao Cao could not afford. After the Battle of Chibi, the Battle of Hanzhong appeared.
The Battle of Hanzhong was initiated by Liu Bei and began in 217 AD and ended in 219 AD, and the entire Battle of Hanzhong lasted for nearly two years. After the Battle of Chibi, Liu Bei regained the counties of Jingzhou, after which Liu Bei wanted to expand further, so there was the basis for the Battle of Hanzhong. Liu Bei, based in Jingzhou, chose to attack Shuchuan.
At the same time, Cao Cao was not idle, and chose to defeat the Guanzhong coalition led by Ma Chao and Han Sui, at which time Cao Cao occupied Hanzhong. After Cao Cao occupied Hanzhong, it put pressure on Liu Bei, shu Han and Hanzhong were the junction, in such a situation, liu Bei can be at ease? Cao Cao's occupation of Hanzhong made Liu Bei uneasy.
Against this background, the Battle of Hanzhong broke out. The entire Battle of Hanzhong lasted for nearly two years, but in the end Cao Cao chose to take the initiative to retreat, why was this? There are many reasons for this. The main reason was that Cao Cao's logistical pressure was too great to support Cao Jun's continued confrontation with Liu Bei.
In the first month of 219, Xiahou Yuan was killed, and Xiahou Yuan's death was undoubtedly a loss to Cao Cao. At that time, when Xiahou Yuan was killed, Cao Cao had already reached Chang'an, so the question was, why did Cao Cao not use to support Xiahou Yuan? Instead, Cao Cao chose to sit in Chang'an. Cao Cao did not need to support Xiahou Yuan, there was something more important.
Now it seems that after the Battle of Hanzhong, Liu Bei did not take advantage of it at all. Cao Cao, who had no need to support Xiahou Yuan, went to pacify the situation in the northwest, when Cao Cao sent Cao Zhang to Pingding, when the northern Wuhuan Wuchen and other troops rebelled, Cao Cao could not be pacified, followed by a rebellion in Wancheng in Jingzhou.
At this time, Cao Cao did not use any extra troops to support Xiahou Yuan. Liu Bei, who had no use of taking advantage, was definitely unwilling, so Liu Bei changed his strategy. Liu Bei saw that Xiahou Yuan was stationed in Hanzhong, so he lured Xiahou Yuan into battle, and in this way, a generation of famous generals fell. After Xiahou Yuan was killed, Liu Bei occupied Hanzhong.
At this time, Liu Bei insisted on not coming out of Hanzhong, and cao Cao's army had no way to do it after it arrived. In ancient times, the war focused on "soldiers and horses did not move, grain and grass first", at that time, Liu Bei chose to garrison Dingjun Mountain, if you want to pass through Dingjun Mountain, you must be able to take Liu Bei. For Cao Cao, Dingjun Mountain was the only way to transport grain and grass.
There are five roads from west to east between Guanzhong and Hanzhong, namely: Qishan Road, ChenCang Road, Chu Chuan Road, Luo Luo Road, and Meridian Valley Road. At this time, Cao Cao wanted to migrate the people, and according to estimates, there were at least 300,000 people who needed to migrate. In this way, Cao Cao certainly gained more than he lost. So Cao Cao gave up such an idea.
You know, in ancient times, population was the primary productive force, and Cao Cao's decision seemed to be nothing, but it was actually unrealistic. Three hundred thousand people want to pass through narrow passages, which is almost impossible. First of all, these people have to eat, just from the grain and grass, it is a big problem. At the end of the Battle of Hanzhong, both sides began to attack each other's grain routes.
To ensure the smooth migration of people, food and grass are indispensable. From this point of view, Cao Cao ensured the smooth migration of the people, then the people of Hanzhong were relocated, and Hanzhong became a wasteland, which was an insignificant place for both Liu Bei and Cao Cao. After the people of Hanzhong were relocated, Hanzhong did not mean much to Cao Cao.
After the population was relocated, Cao Cao changed his strategy, that is, there were no people in Hanzhong, which meant little to Cao Cao. For Cao Cao, the geographical location of Hanzhong is some distance from the Central Plains, so Cao Cao does not value Hanzhong very much, if Cao Cao wants to compete with Liu Bei in Hanzhong, then Cao Cao's logistics must not be able to keep up, so Cao Cao chooses to take the initiative to retreat.
More importantly, Cao Cao's internal problems were also problematic. When Cao Cao came to power, many people in the imperial court resisted him. Although the imperial family of the Eastern Han Dynasty at this time had already existed in name only, fundamentally speaking, the Eastern Han Dynasty still had a foundation. From this point of view, Cao Cao did not dare to fight outside for a long time, otherwise there would be problems within the imperial court.