First, before the Eastern Han regime died, Cao Cao faced internal instability. Although Cao Cao's world was shot down by himself, the role of Emperor Xian of Han Dynasty should not be underestimated. Although the Eastern Han Dynasty was extremely corrupt and the Yellow Scarf Uprising took place, the central government was able to put out the Yellow Scarf Uprising, which proved that the Han Dynasty still had certain organizational ability. For a long time, the rotation of imperial concubines and eunuchs in the Eastern Han Dynasty has actually reached a certain balance, and the court can maintain it for a period of time without any accident.
However, due to general He Jin's low intelligence, this balance was broken, and Dong Zhuo was recruited to lead the troops into Beijing, leading to his death. The two forces, consorts and eunuchs, were beaten to pieces. Dong Zhuo, an outsider, had to control the emperor if he wanted to gain a foothold in the imperial court, so he replaced the emperor Liu Bian and made him thank the emperor. This aroused the dissatisfaction of the heroes in Kanto, so the heroes joined forces to attack Dong Zhuo, and the world began to be in chaos.
In fact, when Dong Zhuo forced Emperor Xian of Han Dynasty to move westward, the Han Dynasty had already perished, but at this time, the Han Dynasty did not perish, and Yu Wei was still there, so Emperor Xian of Han Dynasty still had some value. It is in this situation that Cao Cao welcomed Emperor Xian of Han into his own territory, in order to achieve the goal of "relying on the emperor to make the princes". But it also defines the role of Cao Cao. What is he? He is a courtier of Emperor Xian of Han Dynasty. What is the role of courtiers? Rule the world. So everything he did, on the surface, was for the sake of Emperor Han Xian. As long as Emperor Xian of the Han Dynasty exists, we must constantly pacify the world for him, otherwise it will be dereliction of duty and will be attacked by ministers.
Therefore, if he doesn't go south to collect Jingzhou and fight Battle of Red Cliffs, he must integrate his internal affairs, stand on his own feet on behalf of Emperor Xian of Han Dynasty, and establish his own political power. But this time is not mature, which will inevitably lead to internal chaos. Cao Cao doesn't want to be emperor, but he clearly sees that he can't be emperor, but he can only be king.
Second, the north is not unified. Ma Chao and Han Sui are still very powerful in Kansai. There are Zhang Lu in Hanzhong and Gongsun Kang in Liaodong. Cao can't govern the north with peace of mind. Although Cao Cao defeated Yuan Shao and unified Hebei, Ma Chao and Han Sui were still very powerful in Kansai. Zhang Lu in Hanzhong and Gongsun Kang in Liaodong. They will not let Cao Cao govern the north with peace of mind. It turned out that Ma Chao and Han Sui were difficult to fight. Cao Cao tried to drive Ma Chao away and pacify Guanzhong and Liangzhou, and almost died under Ma Chao.
Zhang Lu in Hanzhong and Gongsun Kang in Liaodong, although not so powerful, can also play the role of harassment at critical moments, so Cao Cao must pacify them if he wants to govern the North with peace of mind. After the pacification, Cao Cao's time waited for no one.
Sun Quan has become a powerful force in Wu Dong, and Liu Bei does not seek Jingzhou with righteousness. If Liu Zhang forces in Yizhou unite against Cao Cao, they can also manage World War I through the efforts of three generations: Sun Jian, Sun Ce and Sun Quan. Wu Dong became the most powerful force against the central government of the Han Dynasty, with internal unity and stability. If Cao Cao leads his troops south to Jingzhou, Sun Quan and Zhou Yu will certainly try their best to annex Jingzhou, and Wu Dong will become stronger then.
However, Jingzhou has complex forces, including Cai Mao brothers supporting Liu Cong and Liu Bei and Liu Qi outside. If Cao Cao doesn't go south, these three parties will inevitably fight with each other. Liu Biao is dead, and Liu Qi's days are not long. If nothing happens, with Zhuge Liang's help, Liu Bei will surely defeat Liu Cong and seize Jingzhou. But the biggest unknown is that Wu Dong will fish in troubled waters and take Jingzhou. But in any case, it is the biggest threat to Cao Cao's reunification of the country.
Liu Bei won Yizhou mainly because Zhang Song and Fazheng lured the wolf into the room. If it weren't for Liu Zhang's initiative to let Liu Bei go to Sichuan to fight Zhang Lu for him, it would not be easy for Liu Bei to enter Yizhou. If Cao Cao attacks Yizhou, Liu Zhang officials and subjects will certainly unite to resist, so it will be difficult for Cao Cao to attack Yizhou, and there will be a fierce battle to fight.
Therefore, even if Cao Cao took Jia Xu's advice and didn't fight Chibi, Cao Cao could not govern the country.
In fact, when Sima Yan ruled the whole country in the Jin Dynasty, the unified war began only when the world was decadent and the local power was very weak, so it was easy to unify. As long as one party can unite with the outside world, it is not easy to unite. During the Cao Cao period, the local governors in the Eastern Han Dynasty were still very strong, and the governance within their jurisdictions was also very different, so the conditions for unifying the world were not yet mature and the time had not yet come. In fact, Cao Cao should fight Ma Chao first, then pacify Yizhou, and then unify Jiangnan when Liu Bei and Sun Quan compete for Jingzhou.