Battle of Chibi
After Cao Cao basically unified the north, he began to make military and political preparations for the southern expedition in the first month of 208. In July, Cao Cao adopted Xun Yu's strategy and personally led a large army to march south to Jingzhou and march towards Wancheng and Ye County. Cao Hong and others were sent to launch a surprise attack from the small road to the east. In September, Cao Hong, the vanguard of the Cao Army, successively broke the Jingzhou Army in Wuyin, Bowang and other places, and the vanguard of the Cao Army had already entered Xinye. Liu Chun panicked, so he accepted the persuasion of Ku Yue and Fu Xun and surrendered to Cao Cao. Liu Bei did not know until Cao Cao's army had reached the vicinity of Wancheng that Liu Chun had surrendered to Cao Cao, and in order to avoid being isolated, he had to immediately abandon Fan and flee south. When Cao Cao heard the news of Liu Bei's departure, he personally led the tiger and leopard to chase Liu Bei with Cao Chun and the Jingzhou general Wen Ping. Cao Jun's tiger and leopard rode in Changsaka to catch up with Liu Bei, so Liu Bei left his wife and children and fled with Zhang Fei, Zhao Yun, Zhuge Liang and dozens of others.
Previously, the forces of Wu Hou and the general who had conquered Jiangdong and the general and consul Taishou Sun Quan were constantly growing. Sun Quan sent Lu Su to Jingzhou to listen to liu bei's intentions and news, and met with Liu Bei at Changsaka in Dangyang to persuade Liu Bei to unite with Sun Quan. Liu Bei met with Guan Yu's water army descending from the east of the Han River, and then encountered more than 10,000 people from Liu Biao's eldest son, Jiang Xia Taishou Liu Qi, who had come to reinforcement, and retreated together to Xiakou on the east bank of the Yangtze River.

Schematic of the Battle of Chibi
Cao Cao used the surrendered Jingzhou water army as the main force in the water battle and prepared for the Eastern Expedition. In October, Cao Cao left Cao Ren to garrison Jiangling and personally led a large army to the east. Zhou Yu led an army to rendezvous with Liu Bei, and the two armies went up against the water and marched to Chibi to meet The Cao army, which was crossing the river. At that time, the Cao army was already plagued, and the newly formed water army and the newly attached Jingzhou water army were difficult to run into, and the morale was obviously insufficient, and the initial battle was defeated by Zhou Yu's water army. Cao Cao pulled his warships to the north shore, and the water army met the army. Zhou Yu docked the warship on the south bank and confronted the Cao army across the Yangtze River.
At that time, Cao Cao was not accustomed to taking a boat for the sake of the Beishishi, so he connected the end and end of the ship, and the people and horses were flat on the ship. Zhou Yu burned the ships connected end to end, and the fire spread to the battalions on the shore. Cao soldiers burned and drowned many people. On the opposite bank, Sun Liu's combined forces crossed the Yangtze River and took advantage of the chaos to defeat the Cao army. Cao Cao saw that the defeat was irreparable, and set himself on fire to the remaining warships and retreated in the direction of Jiangling. Zhou Yu and Liu Bei's armies advanced on land and water, trailing in pursuit. In this battle, Cao Cao's army suffered more than half of the casualties, and after Cao Cao returned to Jiangling, he feared that chibi's defeat would make the rear regime unstable, and immediately returned to the north, leaving Cao Ren and others to continue to stay in Nan Commandery (治所江陵). Sun Liu's combined forces won the Battle of Chibi. The defeat at the Battle of Chibi deprived Cao Cao of the possibility of unifying the country in a short period of time, and Sun and Liu began to develop and expand their respective forces by virtue of this victory.
The biggest beneficiary of the Battle of Chibi was Liu Bei, which laid the foundation for the establishment of the Three Kingdoms and was an important battle that affected the history of the Han people. The smooth situation of Cao Cao's subjugation of Liu Biao's forces was over, the good luck had been reversed before the Battle of Chibi, and Cao Cao's army had a plague on the way forward, which was more effective in weakening Cao Cao's strength and opening Cao Cao's bad luck. Cao Cao's army was strong, while the water army was weak, which was very unfavorable for Cao's army to fight in the vast middle reaches of the Yangtze River, which contributed to the advantage of Cao's army not as large as the ratio of troops between the two sides. Being attacked by Zhou Yu was unexpected, prompting Cao Cao's army to rout. This is a war in which both leaders make fewer obvious mistakes and win more with less. Cao Cao's army was not completely defeated, which was obviously lower than the defeat of the defeating side of the Kunyang Victory and the Battle of Guandu, and Cao Cao's elite troops of tens of thousands of people were not used to be destroyed.
After Cao Cao gained Jingzhou, he could either stabilize it, or he could march into Shu land, or he could move eastward, and no matter how he chose it, it made sense. Stabilizing in Jingzhou is the most conservative decision, the highest safety factor, until Jingzhou is stable, after the people of Jingzhou are consolidated, choose to go east, maybe Cao Cao can smoothly unify the Han region. It is estimated that if Cao Cao did not move his troops in Jingzhou, it would not take long, Liu Bei would most likely clash with Sun Quan, and Cao Jun would be able to take advantage of the fish. If you go west into Shudi, it should also be relatively smooth to subdue the local military and people, and the unification of the Han areas is just around the corner. There is nothing wrong with going east, most of Sun Quan's personnel are in favor of surrendering to Cao's army, which also shows that Sun Quan's chances of surrendering under the pressure of Cao Cao's army are very large, but in the end, it is only Sun Quan who did not choose to surrender, this is just Cao Cao's bad luck. Relatively speaking, going east is a riskier choice, and as a result, these risks are actually reflected (risks are more often not reflected), and Cao Cao's luck at this time is not good.
Map of the division after the Battle of Chibi