< p > In the thirteenth year of Jian'an (208 years), Cao Cao had to return to the north because of the defeat of the Chibi War. Nevertheless, he was unwilling to give up Cao Cao of Jingzhou and left Cao Ren, the first general of Cao's surname, in the most important southern county of Jingzhou to resist the attempt to seize Sun Quan and Liu Bei of Jingzhou.

Cao Ren, who was stationed in Nanjun, was besieged by Zhou Yu, General of Dongwu for nearly a year. Although he had many excellent performances, he still failed to defend Nanjun. But strangely, for as long as a year, Cao Cao had not sent troops to rescue Cao Ren. What's going on here?

First of all, Cao Cao's main army did suffer heavy losses in the battle of Red Cliff, and it was impossible to launch large-scale military operations against the South for a long time afterwards. Therefore, for sending troops to rescue Cao Ren, who has been besieged for a long time, Cao Cao is really powerless.

Secondly, Zhou Yu's attack on Nanjun was not a single action of Dongwu, but a joint action of Sun and Liu. When Zhou Yu besieged Nanjun, Liu Bei sent Guanyu outside Nanjun to stop Cao Jun general near Jingzhou from coming to rescue, and led his own troops to attack Jingzhou County south of Nanjun.

During the year when Cao Ren was besieged, Lejin, Xu Huang, Man Chong, Wen Zheng and other people around Nanjun were restrained by Guan Yu and could not rescue Cao Ren. The only way to break through Guanyu's obstruction was Li Tong, but at that time Zhou Yu had captured Nanjun, and Li Tong only took over Cao Ren's retreat.

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Generally speaking, Cao Ren, who persevered for a year, finally lost the most important southern county in Jingzhou because of the great loss of the Red Cliff War and the tacit understanding of Sun Liu's coalition forces.