Zhuge Liang was Liu Bei's think tank and a famous strategist during the Three Kingdoms period. After Liu Bei got him, he basically laid the world in accordance with his strategic thinking, but made a strategic mistake on the Jingzhou issue, directly laying the foundation for the unification of the three worlds and Cao Wei.
Jingzhou is located in the south of Xuzhou, the west of Jiangdong, and the east of Yizhou. It occupies all of present-day Hubei, Hunan, and Guizhou. Occupying the middle section of the Yangtze River, grain production is abundant. Economic prosperity. But that's only two thousand years later. During the Three Kingdoms period, Jingzhou's economy and grain production were not comparable to those in the Central Plains. Its importance lies in the fact that the population of one million, the Yangtze River Graben, is close to the Central Plains. The really important strategic area was the Central Plains, so zhuge liang and Liu Bei went all out to compete with Sun Quan for Jingzhou, which was a big mistake.
Thirteen years after Jian'an, Cao Cao went south to Jingchu, hoping to unify the world, Zhuge Liang promptly promoted Sun Liu's alliance, Chibi fought, Cao Cao's troops were defeated and returned to the north, Sun and Liu sent troops out of Jingzhou for their own interests, and the jingzhou dispute began.
At first, Lu Su persuaded Sun Quan to borrow Jingzhou and Liu Bei in order to unite against Cao Cao, so Sun Quan borrowed Nan Commandery (南郡) (also known as the Area around Jiangling) to Liu Bei. After that, Liu Bei used Nan Commandery and Jingzhou (except Xiangyang) as his base to capture the four counties of Changsha. He also captured Xichuan and opened up the Shu Han dynasty.
Originally, Liu Bei had the strength to balance the world at this time, but because Guan Yu failed to attack Fancheng, he was secretly attacked by Lü Meng in Jingzhou, and his soldiers were defeated and killed, and the strength of Shu Han was greatly reduced. However, at this time, if you grasp the overall situation well, there is still a chance to revitalize the national strength, but you do not want to be like Liu Bei. Even if jingzhou can be recaptured, it is not possible to send troops to attack Wu, so even if jingzhou is recaptured, it will fall into the situation of two-front combat.
Liu Bei seized Jingzhou because once shu Han lost Jingzhou, it would become a small country that defended itself. Therefore, he needs to retake the frontier of a Shu Han dynasty. But both he and Zhuge Liang forgot that Shu had another frontier, Guanzhong.
Jingzhou had been lost, and instead of spending national strength to compete, it was better to send Sun Quan a favor by pushing a boat along the water and asking him to send troops to attack Xuzhou or Hefei. After Sun Quan won Jingzhou, it was difficult to take Sichuan, and it was inevitable that the north would fight for Xuzhou. Even if it does not send troops immediately, it will pose a threat to Xuzhou. Liu Bei took the opportunity to leave Qinchuan, with Ma Chao as the vanguard, to capture Longxi, form a good alliance with the Qiang people, refuse to defend the pass, and sort out internal affairs. When the world changes, it will gallop through the Central Plains with elite soldiers. It is not yet known whose hand the deer died.
In fact, as early as the time of the capture of Yizhou, Liu Bei should return Sun Quannan County. This was the only place where Sun Quan lent Liu Bei, and after returning it, Liu Bei was no longer at a loss on the Jingzhou issue. He also asked Sun Quan to attack Hefei and fight for Hanzhong himself. Then Jiang Xia gave Sun Quan, asked him to attack Xuzhou, attack Longxi himself, and then wait for the world to change, with the main force to capture the Central Plains, Guan Yu to contain Sun Quan's troops, then the opportunity for unification is still large.