In 214, Liu Bei broke up Liu Zhang in the Sichuan-Shu region, so in order to counter Liu Zhang, he recalled Zhao Yun, Zhang Fei, and Zhuge Liang, leaving Guan Yu alone in Jingzhou. In order to be able to better confront Liu Zhang, most of the Shu state's troops were transferred to Sichuan shu, leaving only a small number of troops to defend Jingzhou.
However, in 219 AD, there was a turning point in the history of the Three Kingdoms- Cao Cao and Sun Quan secretly attacked Jingzhou, causing Guan Yu to carelessly lose Jingzhou and defeat Maicheng, and was captured and killed by the Wu army. In fact, Guan Yu's death lies in the individual, once Zhuge Liang was ordered to enter Sichuan Shu when he left such a sentence for Guan Yu: "East and Sun Quan, North reject Cao Cao." This sentence is very easy to understand that the Shu state has always used to unite with Sun Quan against the State of Wei, and it can be said that the alliance of Sun Liu is the fundamental condition for opposing the State of Wei. Then the sparse number of troops to defend Jingzhou alone to guan yu must be to unite with Sun Quan. The strength of the State of Wei was the strongest of the Three Kingdoms, and it was even more impossible to unite him.
After Guan Yu transferred most of the troops of the Shu state into Sichuan and Shu, he immediately gathered a small number of soldiers and horses from Jingzhou to attack Fancheng. Cao Ren, who was guarding Fancheng, did not expect Guan Yu to be so bold and had no use for defense at all, and he lost several battles in succession. Fancheng was the front line of the Wei capital Xu Du once Xu Du was lost, so Cao Cao sent the Forbidden Seventh Army to support Fancheng. At that time, the low-lying area of Yu Ban camp was flooded by Guan Yu. At this time, the panicked Cao Cao was able to find a way to unite with the State of Wu and let the State of Wu sneak up on Guan Yu in order to relieve the crisis.
Sun Quan was later persuaded to sneak up on Guan Yu, but it was not good to tear his face when the Sun Liu Alliance existed for many years. So Sun Quan wanted to marry Guan Yu's daughter back in order to consolidate the alliance front. However, Guan Yu looked down on Sun Quan at all, and at the same time forgot the words of "Donghe Sun Quan" after the military division left. Directly humiliating Sun Quan with the phrase "tiger women do not marry dogs", Sun Quan is a noble prince of a country, and Guan Yu, who can tolerate such humiliation, sends troops to sneak into Jingzhou. Guan Yu thus led to the defeat of Maicheng and was killed by the Wu army.
In fact, Zhuge Liang had already given Guan Yu advice to defend Jingzhou alone, but Guan Yu did not need to understand. Originally, Guan Yu made a beautiful account under unexpected circumstances, and even almost forced Cao Cao to abandon Xu Du, in fact, from this it can be seen that Guan Yu's general talent is. However, Guan Yu did not face up to Sun Liu's alliance and led to his being attacked by Sun Quan. Even later Guan Yu was defeated and asked for help from Lü Meng, and Lü Meng separated the army. Cao Cao exchanged Jiangnan for the disintegration of Sun Liu's alliance.