First, for the ownership of Jingzhou, Liu Bei and Sun Quan almost broke out in war.
In 2 14, after three years of fighting, Liu Bei finally entered Chengdu and occupied Xichuan area. When Sun Quan learned of it, he immediately sent messengers to beg for Jingzhou. Jingzhou is very important to Liu Bei Group. Zhuge Liang's development strategy for Liu Bei was to take Jingzhou and Xichuan as the capital, and then make two northern expeditions. Liu Bei's series of tactical actions are all around this strategic plan. Now that Sun Quan has arrived in Jingzhou, Liu Bei certainly didn't mean it to him. At that time, Jingzhou had less than 40 thousand troops, and Liu Bei was worried that Guan Yu could not keep Jingzhou. While Hanzhong in the north is still in the hands of Zhang Lu, Liu Bei is not worried about the threat from the north for the time being. Liu Bei personally led 50,000 troops to reinforce Jingzhou. Once Sun Quan wants to do it, Liu Bei is ready to beat Sun Quan up. Judging from the situation at that time, Liu Bei had this strength. But at this time, Cao Cao attacked Hanzhong on a large scale, so Cao Cao is likely to win by surprise. This forced Liu Bei to quit Li halfway and make peace with Sun Quan.
In order to stabilize Sun Quan, Liu Bei ceded a part of Jingzhou to Sun Quan, and both sides were very depressed. Before Liu Bei returned to Chengdu, Cao Cao had quickly captured Hanzhong. At this time, both Liu Bei and Sun Quan thought that Cao Cao would attack Xichuan south, so Liu Bei actively prepared for the war, and his foundation in Xichuan was not stable. On Sun Quan's side, Lu Su, the number one counselor, has always suggested uniting against Cao. Now that Cao Cao is going to attack Xichuan, Lu Su thinks it is time to seize Xuzhou under Cao Cao's control. Egged on by Lu Su, Sun Quan personally commanded the army to advance northward. But he met his powerful rival Zhang Liao, and Sun Quan's army failed to advance. What's more, Cao Cao gave up his plan to attack Xichuan and led the main force to reinforce Huaibei area. After the fierce fighting between the two sides, Sun Quan hastily retreated with nothing.
Second, the death of Lu Su led to the turmoil of the Sun-Liu Alliance.
In 2 17, Lu Su, who had always advocated an alliance, died and the hardliner Monroe came to power. This directly cast a shadow over the Sun-Liu Alliance and added a sense of crisis to Jingzhou. At the beginning of Monroe's coming to power, Liu Bei was attacking Hanzhong with all his strength, and Cao Cao also led troops to reinforce him. The two main groups attacked Hanzhong, and Sun Quan took the initiative. At that time, Jingzhou and Xuzhou were short of troops. Sun Quan asked Monroe where to attack. Monroe thought it was easy to capture Xuzhou, but Xuzhou was flat and unguarded. If you want to hold it completely, you need 70,000 to 80,000 troops. This did more harm than good to Sun Quan Group, so Monroe suggested attacking Jingzhou area. After the occupation of Jingzhou, you can use the Yangtze River to block Cao Cao in the north, or you can completely seal Liu Bei in the Three Gorges. Sun Quan agreed with Monroe's suggestion, but Guan Yu, the commander in chief of Jingzhou, was not easy to deal with, so he was biding his time.
In 29 years, the two sides fought three wars, and Liu Bei defeated Cao Cao and captured Hanzhong. After Liu Bei captured this area, he was in a favorable position to advance, attack and retreat. This autumn, Liu Bei proudly claimed to be the king of Hanzhong and began to compete with Cao Cao. But Liu Bei's peak only lasted less than four months. This winter, Guan Yu, the general of Jingzhou, led the main army of Jingzhou to attack Cao Cao actively. At that time, the total strength of Jingzhou was less than 40,000, and Guan Yu moved northward to transfer nearly 30,000 soldiers. But in the face of well-prepared Cao Cao, Guan Yu's military action was not smooth. Guan Yu's mistakes on diplomatic issues completely angered Sun Quan. When the army was short of rations, Guan Yu ordered to enter Sun Quan's control area to collect rations. Sun Quan is very unhappy. He reached an agreement with Cao Cao and ordered Monroe to attack Jingzhou.
After losing Jingzhou, Liu Bei Group suffered heavy losses.
After Lu Su's death, Liu Bei Group should start thinking about defending Jingzhou. However, due to the great threat from Hanzhong, Liu Bei could not give up, so he could only temporarily weaken Jingzhou's defense and attack Hanzhong with all his strength. After the victory in Hanzhong, Liu Bei's main force was in urgent need of rest and did not return to Jingzhou in time. Jingzhou was successfully captured by Monroe, and Guan Yu was captured by Cao Cao and Sun Quan. Guan Yu was defeated and killed. The fall of Jingzhou means that Liu Bei can only attack Cao Cao from Xichuan, and the success rate of this plan is not high. So Liu Bei had to recapture Jingzhou. More than a year after Guan Yu was killed, Liu Bei assembled more than 60 thousand domestic elite troops to attack Sun Quan. However, Fazheng, Zhang Fei and Huang Zhong are all dead, Ma Chao and Wei Yan want to defend Cao Cao, and Liu Bei has no reliable civil servants and military commanders. It is still possible to deal with second-rate generals at Liu Bei's own level. For the famous general, he will only be beaten up.