The so-called enemy of ten thousand people refers to Guan Yu's military ability. Just watching him kill Yan Liang in the Battle of White Horse can be regarded as a unique act of killing the enemy in the Three Kingdoms. At that time, Zhang Liao and Guan Yu were both forwards of Cao Cao, and only Guan Yu personally beheaded Yan Liang, which was Guan Yu's bravery.
Guan Yu's success in Xiangfan is also a manifestation of his military ability. With the help of the three counties in Jingzhou, Cao Cao was incited to the whole Central Plains, which made people in the Central Plains panic. Those who were dissatisfied with Cao Cao's rule in the Central Plains, rose up against Cao Cao and took refuge in Guan Yu, such as Lu Hun, Hou Yin, Kai Wei, Jingzhou secretariat Hu Xiu and others, all took refuge in Guan Yu because Guan Yu was too powerful.
Cao Cao mobilized almost half of Cao Wei's troops to deal with Guan Yu. If Sun Quan hadn't attacked Jingzhou, it would have been difficult for Cao Cao to defeat Guan Yu. If Guan Yu was captured by Cao Cao and directly took refuge in Cao Cao, would history change? How will it change?
If Liu Bei did not have Guan Yu, it would be a great loss. First of all, Liu Bei wants to divide his troops and has no reliable generals. Although Zhang Fei is as famous as Guan Yu, his ability is far from perfect. He not only likes to abuse foot soldiers, but also guards Xiapi City, which is easily breached by Lu Bu. Without Guan Yu, Liu Bei would not have an independent general.
Without Guan Yu, although Liu Bei could occupy the four counties in Jingnan and borrow Nanjun from Sun Quan, only Zhang Fei would keep Jingzhou. If Zhang Fei holds Jingzhou, I estimate that Jingzhou may fall earlier, and even Yizhou may not be captured, because Liu Bei was not so ordinary at first, and Wei Yan, Huang Zhong and others all appeared later.
If Guan Yu and Cao Cao were together, even if Battle of Red Cliffs failed, if Guan Yu had been guarding Jiangling City in Nanjun County, it would not be so easy to lose. With the strong support of Cao Cao, Guan Yu will certainly create greater achievements, at least not as good as Guan Yu, and Guan Yu may grow into Cao Cao's first physics general.
If Cao Cao takes Guan Yu as the goal to conquer Jingzhou or Sun Quan, he will certainly achieve something, at least much better than Cao Cao's personal expedition. Guan Yu is a very shrewd man. After staying in Jingzhou for several years, northerners trained a water army. It is very likely that Guan Yu will help Cao Cao defeat Liu Bei and Sun Quan, and it is also possible to unify the world. What Guan Yu lacks is actually the support of opportunity and strength.
If Guan Yu is a subordinate of Cao Cao, he can go one step further and become a senior general of Cao Wei, and Zhang Liao will be excluded, but in this way, Guan can't be a warrior in the history of China.