In 219, Liu Bei defeated Cao Cao and thus captured Hanzhong, after which, in order to continue his rebellion against Cao Cao, Liu Bei established himself as the king of Hanzhong and made Guan Yu, who was sitting in Jingzhou, a former general. Perhaps at the suggestion of Liu Bei, after being appointed as a former general, Guan Yu immediately sent an army to conquer Cao Wei, and he led his army all the way north to besiege Xiangfan, and after that, the Seventh Army flooded, and for a time, Guan Yu's momentum shocked Huaxia. Originally, Guan Yu could have taken this opportunity to conquer Xiangfan and go deep into the hinterland of Cao Wei, but at this time, the overall strength of Shu Han was hidden to surpass Eastern Wu, and in order to avoid Shu Han becoming bigger, Sun Quan sent Lü Meng to cross the river in white clothes, taking advantage of the emptiness of Jiangling to seize Jiangling and occupy Guan Yu's rear, causing Guan Yu's army to be defeated and retreat to Maicheng. In order to completely kill Guan Yu, Sun Quan set up layers of encirclement in Jingzhou, captured Guan Yu, and then killed him.
After Sun Quan backstabbed Guan Yu and captured Jingzhou, Liu Bei was furious, and two years later, Liu Bei ascended the throne as emperor and immediately launched a war against Eastern Wu. Although in the early stages of the war, Liu Bei once attacked the area of Zigui and invaded Yiling, but because Lu Xun waited for work and took advantage of the Shu army to relax its vigilance, he suddenly launched an attack, and burned the camp for seven hundred miles, completely defeating the Shu army. The Shu army collapsed and almost completely withdrew from the ranks of the world. After Liu Bei's death, Zhuge Liang and the animals were reconciled, which shows that Eastern Wu and Shu Han can continue to ally. So after Sun Quan backstabbed Guan Yu and captured Jingzhou, did Liu Bei have any other choice than to launch a war?
In fact, at that time, Liu Bei had no other choice but to launch a war against Eastern Wu. It should be known that Lü Meng's original plan was not just to occupy Jingzhou, in Lü Meng's vision, he wanted to occupy Jingzhou first, and then use the advantage of "all according to the Yangtze River" to send troops to Shu Han to achieve the goal of conquering the White Emperor City, and finally destroy Shu Han and divide the world with Cao Wei, so that Eastern Wu had the possibility of defeating Cao Wei, just because at that time, Eastern Wu's plan was already to destroy Shu Han, so Liu Bei had to fight at that time.
What's more, when Liu Bei attacked Yizhou before, Sun Quan sent troops to fight for Jingzhou, after which Liu Bei led his army back to help, Cao Cao attacked Hanzhong, Liu Bei had no choice but to cross the Xiang River with Sun Quan and rule, and later Guan Yu northern expedition, Sun Quan captured Jingzhou. That is to say, if Liu Bei still trusted Eastern Wu and attacked Yongliang after claiming the title of emperor, then Sun Quan could take this opportunity to send an army to attack Shu Han, and when Liu Bei was attacked by the enemy, it might be the time when Shu Han was about to perish. Because the hatred between Liu Bei and Sun Quan was greater at that time, Liu Bei was destined to attack Eastern Wu.
The author believes that in addition to the general situation in the world at that time, Liu Bei's personal feelings also need to be considered, after all, Guan Yu and Liu Bei have deep feelings, and it is also reasonable for Liu Bei to avenge Guan Yu and send troops to attack Eastern Wu, so Liu Bei had no choice but to attack Eastern Wu at that time.