The decreasing strength of the Cao clan was mirrored by the decline of Shu. After Zhuge Liang's death, his position as chancellor fell to Jiang Wan, Fei Yi and Dong Yun, in that order. But after 258, Shu politics became increasingly controlled by the eunuch faction and corruption rose. Despite the energetic efforts of Jiang Wei, Zhuge Liang's protege, Shu was unable to secure any decisive achievement. In 263, Wei launched a three-pronged attack and the Shu army was forced into general retreat from Hanzhong. Jiang Wei hurriedly held a position at Jiange but he was outflanked by the Wei commander Deng Ai, who force-marched his army from Yinping through territory formerly considered impassable. By the winter of the year, the capital Chengdu fell due to the strategic invasion of Wei by Deng Ai who invaded Chengdu personally. The emperor Liu Shan thus surrendered. The state of Shu had come to an end after 43 years.

From the late 230s tensions began to become visible between the imperial Cao clan and the Sima clan. Following the death of Cao Zhen, factionalism was evident between Cao Shuangand the Grand Tutor Sima Yi. In deliberations, Cao Shuang placed his own supporters in important posts and excluded Sima Yi, whom he regarded as a dangerous threat. The power of the Sima clan, one of the great landowning families of the Han Dynasty, was bolstered by Sima Yi's military victories. Additionally, Sima Yi was an extremely capable strategist and politician. In 238 he crushed the rebellion of Gongsun Yuan and brought the Liaodong region directly under central control. Ultimately, he outmaneuvered Cao Shuang in power play. Taking advantage of an excursion by the imperial clansmen to the Gaoping Tombs, Sima Yi undertook a putsch in Luoyang, forcing Cao Shuang's faction from authority. Many protested against the overwhelming power of the Sima family; notable among these were the Seven Sages of the Bamboo Grove. One of the sages, Xi Kang, was executed as part of the purges after Cao Shuang's downfall.

In the times of Zhuge Liang's northern offensives, the state of Wu had always been on the defensive against invasions from the north. The area around Hefei was the scene of many bitter battles and under constant pressure from Wei after the Battle of Red Cliffs. Warfare had grown so intense that many of the residents chose to migrate and resettle south of the Yangtze River. After Zhuge Liang's death, attacks on the southern Huai River region intensified but nonetheless, Wei could not break through the line of the river defenses erected by Wu, which included the Ruxu fortress.

Sun Quan's long reign is regarded as a time of plenty for his southern state. Migrations from the north and the settlement of the Shanyue increased manpower for agriculture, especially along the lower reaches of the Yangtze and in Kuaiji commandery (present-day Shaoxing). River transport blossomed, with the construction of the Zhedong and Jiangnan canals. Trade with Shu flourished, with a huge influx of Shu cotton and the development of celadon and metal industries. Ocean transport was improved to such an extent that sea journeys were made toManchuria and the island of Taiwan. In the south, Wu merchants reached Linyi (northern Vietnam) and Fu'nan (Cambodia). As the economy prospered, so too did the arts and culture. In the Yangtze delta, the first Buddhist influences reached the south from Luoyang.

At the end of Zhuge Liang's Southern Campaign, the Wu-Shu alliance came to fruition and Shu was free to move against the north. In 227 Zhuge Liang transferred his main Shu armies to Hanzhong, and opened up the battle for the northwest with Wei. The next year, he orderedZhao Yun to attack from Ji Gorge as a diversion while Zhuge himself led the main force to Mount Qi. The vanguard Ma Su, however, suffered a tactical defeat at Jieting and the Shu army was forced to withdraw. In the next six years Zhuge Liang attempted several more offensives, but supply problems limited the capacity for success. In 234 he led his last great northern offensive, reaching the Battle of Wuzhang Plains south of the Wei River. Due to the death of Zhuge Liang (234), however, the Shu army was forced once again to withdraw, but were pursued by Wei. The Shu forces began to withdraw; Sima Yi deduced Zhuge Liang's demise and ordered an attack. Shu struck back almost immediately, causing Sima Yi to second guess and allow Shu to withdraw successfully.

In 223 Liu Shan rose to the throne of Shu following his father's defeat and death. The defeat of Liu Bei at Xiaoting ended the period of hostility between Wu and Shu and both used the opportunity to concentrate on internal problems and the external enemy of Wei. For Sun Quan, the victory terminated his fears of Shu expansion into Jing Province and he turned to the aborigines of the southeast, whom the Chinese collectively called the "Shanyue". A collection of successes against the rebellious tribesmen culminated in the victory of 224. In that year Zhuge Ke ended a three year siege of Danyang with the surrender of 100,000 Shanyue. Of these, 40,000 were drafted as auxiliaries into the Wuarmy. Meanwhile Shu was also experiencing troubles with the indigenous tribes of their south. The southwestern Nanman peoples rose in revolt against Shu authority, captured and looted cities in Yi Province. Zhuge Liang, recognising the importance of stability in the south, ordered the advance of the Shu armies in three columns against the Nanman. He fought a number of engagements against the chieftain Meng Huo, at the end of which Meng Huo submitted. A tribesman was allowed to reside at the Shu capital Chengdu as an official and the Nanman formed their own battalions within the Shu army.

In the first month of 220, Cao Cao died and in the tenth month his son Cao Pi forced Emperor Xian to abdicate, thus ending the Han Dynasty. He named his state Wei and proclaimed himself emperor in Luoyang. In 221, Liu Bei declared himself emperor, in a bid to restore the fallen Han Dynasty. (His state is known in history as "Shu" or "Shu Han") In the same year, Wei bestowed on Sun Quan the title of King of Wu. A year later, Shu declared war on Wu and met the Wu armies at the Battle of Xiaoting (also known as Battle of Yiling). At Xiaoting, Liu Bei was disastrously defeated by Sun Quan's commander Lu Xun and forced to retreat back to Shu, where he died soon afterward. After the death of Liu Bei, Shu and Wu resumed friendly relations at the expense of Wei, thus stabilizing the tripartite configuration. In 222, Sun Quan renounced his recognition of Cao Pi's regime and, in 229, he declared himself emperor of Eastern Wu in Wuchang.

Dominion of the north completely belonged to Wei, whilst Shu occupied the southwest and Wu the central south and east. The external borders of the states were generally limited to the extent of Chinese civilization. For example, the political control of Shu on its southern frontier was limited by the Tai tribes of present-day Yunnan and Burma, known collectively as the "Nanman" (southern barbarians).

In 208, Cao Cao marched south with his army hoping to quickly unify the empire. Liu Biao's son Liu Cong surrendered Jing Province and Cao was able to capture a sizable fleet at Jiangling. Sun Quan, the successor to Sun Ce in the lower Yangtze, continued to resist, however. His advisor Lu Su secured an alliance with Liu Bei, himself a recent refugee from the north, and Zhou Yu was placed in command of Sun Quan's navy, along with a veteran general who served the Sun family, Cheng Pu. Their combined armies of 50,000 met Cao Cao's fleet and 200,000-strong force at Red Cliffs 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 King of Wei in 217, a title bestowed upon him by the puppet Emperor Xian that he controlled. Liu Bei, having defeated the weak Jing Province warlords Han Xuan, Jin Xuan, Zhao Fan, and Liu Du, entered Yi Province and later in 214 displaced Liu Zhang as ruler, leaving 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 Yangtze. 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 Fancheng, Sun Quan's general Lü Meng seized Jing Province in a surprise invasion. Guan Yu was captured and executed on Sun Quan's order.

After settling the nearby provinces, including a rebellion led by former Yellow Turbans, and internal affairs with the court, Cao Cao turned his attention north to Yuan Shao, who himself had eliminated his northern rival Gongsun Zan that same year. Yuan Shao, himself of higher nobility than Cao Cao, amassed a large army and camped along the northern bank of the Yellow River.

In 200, after winning a decisive battle against Liu Biao at Sha County and putting down the rebellions of Xu Gong and others, Sun Ce was struck by an arrow and fatally wounded. On his deathbed, he named his younger brother, Sun Quan, as his heir.

Following months of planning, Cao Cao and Yuan Shao clashed at the Battle of Guandu. Overcoming Yuan Shao's superior numbers, Cao Cao decisively defeated him by setting fire to his supplies, and in doing so crippled the northern army. Liu Bei fled to join Liu Biao in Jing Province, and many of Yuan Shao's forces were destroyed. In 202, Cao Cao took advantage of Yuan Shao's death and the resulting division among his sons to advance north of the Yellow River. He captured Ye in 204 and occupied the provinces of Ji, Bing, Qing and You. By the end of 207, after a lightning campaign against the Wuhuan barbarians, Cao Cao had achieved undisputed dominance of the North China Plain.

In the south, Sun Ce, then an independent general under the service of Yuan Shu, defeated the warlords of Yang Province, including Liu Yao,Wang Lang, and Yan Baihu. In 197, Yuan Shu, who was at odds with Cao Cao, Yuan Shao, and Liu Bei, felt assured of victory with his subordinate's conquests, and thus declared himself emperor of the Cheng Dynasty. The move, however, was a strategic blunder, as it drew the ire of many warlords across the land, including Yuan Shu's own subordinate Sun Ce, who had advised Yuan Shu not to make such a move. Cao Cao issued orders to Sun Ce to attack Yuan Shu. Sun Ce complied, but first convinced Cao Cao to form a coalition against Yuan Shu, of which Liu Bei and Lü Bu were members. Attacked on all sides, Yuan Shu was defeated and fled into hiding.

Afterwards, Lü Bu betrayed Liu Bei and seized Xu Province, forming an alliance with Yuan Shu's remnant forces. Liu Bei, together with his followers Zhang Fei and Guan Yu, fled to Cao Cao, who accepted him. Soon, preparations were made for an attack on Lü Bu, and the combined forces of Cao Cao and Liu Bei invaded Xu Province. Lü Bu's men deserted him, Yuan Shu's forces never arrived as reinforcements, and he was bound by his own subordinates Song Xian and Wei Xu and executed on Cao Cao's order.

In 200, Dong Cheng, an imperial relative, received a secret edict from Emperor Xian to assassinate Cao Cao. He collaborated with Liu Bei on this effort, but Cao Cao soon found out about the plot and had Dong Cheng and his conspirators executed, with only Liu Bei surviving and fleeing to join Yuan Shao in the north.

In 191, there was some talk among the coalition of appointing Liu Yu, an imperial relative, as emperor, and gradually its members began to fall out. Most of the warlords in the coalition, with a few exceptions, sought the increase of personal military power in the time of instability instead of seriously wishing to restore the Han Dynasty's authority. The Han empire was divided between a number of regional warlords. Yuan Shao occupied the northern area of Ye and extended his power, by taking over his superior Han Fu with trickery and intimidation, north of theYellow River against Gongsun Zan, who held the northern frontier. Cao Cao, directly to Yuan Shao's south, was engaged in a struggle against Yuan Shu and Liu Biao, who occupied respectively the Huai River basin and middle Yangtze regions. Further south the young warlord Sun Ce, taking over after the untimely death of Sun Jian, was establishing his rule in the lower Yangtze, albeit as a subordinate of Yuan Shu. In the west, Liu Zhang held Yi Province while Hanzhongand the northwest were controlled by a motley collection of smaller warlords such as Ma Teng of Liang Province, the original post of Dong Zhuo.

Dong Zhuo, confident in his success, was slain by his follower Lü Bu and minister Wang Yun. Lü Bu, in turn, was attacked by Dong Zhuo's subordinates: Li Jue, Guo Si, Zhang Ji and Fan Chou. Wang Yun and his whole family were executed. Lü Bu fled to Zhang Yang, a northern warlord, and remained with him for a time before briefly joining Yuan Shao, but it was clear that Lü Bu was far too independent to serve another.

In August 195, Emperor Xian fled the tyranny of Li Jue at Chang'an and made a year long hazardous journey east in search of supporters. By 196, when he was received by Cao Cao, most of the smaller contenders for power had either been absorbed by larger ones or destroyed. This was an extremely important move for Cao Cao following the suggestion from his primary advisor, Xun Yu, commenting that by supporting the authentic emperor, Cao Cao would have the formal legal authority to control the other warlords and force them to comply in order to restore the Han Dynasty.

Cao Cao, whose zone of control was the precursor to the state of Cao Wei, had raised an army in the winter of 189. In several strategic movements and battles, he controlled Yan Province and defeated several factions of the Yellow Turban rebels. This earned him the aid of other local militaries controlled by Zhang Miao and Chen Gong, who joined his cause to create his first sizable army. He continued the effort and absorbed approximately 300,000 Yellow Turban rebels into his army as well as a number of clan-based military groups from the eastern side of Qing Province. In 196 he established an imperial court at Xuchang and developed military agricultural colonies (tuntian) to support his army. Although the system imposed a heavy tax on hired civilian farmers (40% to 60% of agricultural production), the farmers were more than pleased to be able to work with relative stability and professional military protection in a time of chaos. This was later said to be his second important policy for success.

In 194, Cao Cao went to war with Tao Qian of Xu Province, because Tao's subordinate Zhang Kai had murdered Cao Cao's father Cao Song. Tao Qian received the support of Liu Bei and Gongsun Zan, but even then it seemed as if Cao Cao's superior forces would overrun Xu Province entirely. However, Cao Cao received word that Lü Bu had seized Yan Province in his absence, and accordingly he retreated, putting a halt to hostilities with Tao Qian for the time being. Tao Qian died in the same year, leaving his province to Liu Bei. A year later, in 195, Cao Cao managed to drive Lü Bu out of Yan Province. Lü Bu fled to Xu Province and was received by Liu Bei, and an uneasy alliance began between the two.