Red Cliffs and its aftermath

In 208, Cao Cao marched south with his army hoping to quickly unify the empire. Liu Biao's son Liu Cong surrendered the province of Jing and Cao was able to capture a sizeable fleet at Jiangling. Sun Quan, the successor to Sun Ce in the Lower Yangzi, continued to resist however.

 His advisor Lu Su secured an alliance with Liu Bei, himself a recent refugee from the north, and Sun Ce's sworn brother Zhou Yu was placed in command of Sun Quan's navy, along with a veteran officer of the Sun family, Cheng Pu. Their combined armies of 50,000 met Cao Cao's fleet and 200,000-strong force at Red Cliffs (Chinese: 赤壁 Chi Bi) that winter.

 After an initial skirmish, an attack beginning with a plan to set fire to Cao Cao's fleet was set in motion to lead to the decisive defeat of Cao Cao, forcing him to retreat in disarray back to the north. The allied victory at Red Cliffs ensured the survival of Liu Bei and Sun Quan, and provided the basis for the states of Shu and Wu.

After his return to the north, Cao Cao contented himself with absorbing the northwestern regions in 211 and consolidating his power. He progressively increased his titles and power, eventually becoming the Prince of Wei in 217, a title bestowed upon him by the puppet Han emperor that he controlled. Liu Bei, having defeated the weak Jing warlords Han Xuan, Jin Xuan, Zhao Fan, and Liu Du, entered Yi province and later in 214 displaced Liu Zhang as ruler, leaving his commander Guan Yu in charge of Jing province. Sun Quan, who had in the intervening years being engaged with defenses against Cao Cao in the southeast at Hefei, now turned his attention to Jing province and the Middle Yangzi.

Tensions between the allies were increasingly visible. In 219, after Liu Bei successfully seized Hanzhong from Cao Cao and as Guan Yu was engaged in the siege of Fan, Sun Quan's commander-in-chief Lu Meng secretly seized Jing province, and his forces captured and slew Guan Yu.