Actor Cao Cao immigrated to Spain.

Although Cao Cao's voluntary withdrawal was influenced by external factors such as the critical situation in the northwest border, the military pressure in Jingzhou, the central line and the internal rebellion, the main reason was that Cao Cao could no longer confront Liu Bei in Hanzhong because of the huge logistical pressure. Xia was killed in January of 2 19. In fact, Cao Cao arrived in Chang 'an in September of February18. After Cao Cao arrived in Chang 'an, he did not go south to Hanzhong to support Xia, but sat in Chang 'an to observe the situation.

Why didn't Cao Cao immediately go south to Hanzhong to support Xia? Because Cao Cao has more important things to do, and Cao Cao thinks that Liu Bei can't take advantage of Hanzhong as long as Xiahou Yuan sticks to the right thing. In fact, the battle of Hanzhong began in 2 17, and Liu Bei has not taken advantage of it in these two years. In fact, Cao Cao was on his way to Chang 'an, Yecheng, and the northern Wuhuan, a transit country in the northwest of Cao Wei, rebelled. Cao Cao sent Cao Zhang to suppress it. When the situation in the northwest was not completely clear, in June of 20 18, there was a rebellion in Wancheng, Jingzhou, and Wei Kai and Hou Yin, the garrison commanders of Wancheng, could not stand the heavy taxes imposed by Cao Wei. Cao Cao rebelled against the city.

Originally, Liu Bei didn't take advantage of the battle in Hanzhong. If Baishuiguan attacked Hanzhong from Chengdu, Yangpingguan was the first pass, and Liu Bei could not win Hanzhong. However, Liu Bei changed his tactics from the first month of 2 19. Liu Bei crossed Micang Mountain, where there was no way out, and appeared to the east of Yangpingguan, which was behind Xiahou Yuan. Liu Bei lured Xia Da, and then killed Xia with a trick. So Cao Cao led a great army and began to March to Hanzhong. After 1 month's March, Cao Cao entered Hanzhong through a 500-mile-long ramp, then entered Yangpingguan along the Hanshui River and began to confront Liu Bei, but Liu Bei refused to play at this time.

Dingjun Mountain, where Liu Bei is stationed, is in a very good position, on the south bank of Hanshui River between Yangpingguan and Caocao Liangdao. If Cao Cao wants to use the Han River to transport food, he must pass Liu Bei's camp in Dingjun Mountain. In order to prevent Liu Bei from attacking his own camp, Cao Cao also sent troops to Dingjun Mountain to confront Liu Bei, and both sides were attacking each other's route for providing foodstuff. Not long after Cao Cao arrived in Yangpingguan, he began to transfer the people of Hanzhong to Guanzhong and the Central Plains. From Guanzhong to Hanzhong, there are five roads from west to east, namely: Qishan Road, Chencang Road, Xiexie Road, Luo Luo Lu Road and Woods Valley Road. Cao Cao moved a lot of people, it is said that there are at least 300 thousand.

In troubled times, population is the primary productive force and the foundation of everything. At that time, there was no shortage of land and people. With population, there is everything. Therefore, Cao Cao often does this kind of thing, and it is not easy to resettle 300,000 people. It is a very difficult and complicated project for so many people to go to Guanzhong through these five roads. In fact, these people are unwilling to move. If they move, they will lose many things, including land and houses, livestock, grain and treasures. It is conceivable that 300,000 people passed through those narrow passages. What a complicated project this is. These people want to eat. Cao Cao Can couldn't let them starve to death, so he had to provide food and grass, which is why Cao Cao collapsed.

At the end of the battle of Hanzhong, Cao Cao and Liu Bei attacked each other for providing foodstuff. As a result, Cao Cao failed, but Liu Bei succeeded in capturing Cao Cao's route for providing foodstuff in Hanshui, which made Cao Cao unbearable. The food supply of so many people is suddenly tight, and many soldiers run away with the refugees every day. Moreover, in order to ensure the smooth migration of 300,000 yuan, all the increased expenses will fall on the farmers in the border areas of Cao and Wei, and the people will be even more dissatisfied. Cao Cao really can't stay in Hanzhong.

On the one hand, soldiers escape every day, the morale is unstable, and the war situation is deadlocked; On the other hand, the huge logistical pressure makes Cao Cao breathless, and if this continues, it will trigger a greater wave of opposition in Guanzhong area. Finally, Cao Cao has moved most of the people in Hanzhong. Hanzhong is of little significance to Cao Cao, what's more, there is a very difficult 800-mile Qinchuan between Hanzhong and Guanzhong!

2/kloc-in may of 0/9, news of Guan Yu's advance came from Jingzhou front, and Cao Cao finally retreated. On the way back, even 300,000 people have not yet left, and Cao Cao's retreat is in chaos. Military and civilian mixed together, I don't know how many people died on the road.