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.

While Dong Zhuo originally wanted to re-establish the authority of the Han Dynasty and manage all the political conflict properly, his political capability proved to be much worse than his military leadership. His behaviour grew more and more violent and authoritarian, executing or sending into exile all that opposed him, and showed less and less respect to the emperor. He ignored all royal etiquette and frequently carried open weapons into the imperial court. In 190 a coalition led by Yuan Shao was formed between nearly all the provincial authorities in the eastern provinces of the empire against Dong Zhuo. The mounting pressure from repeated defeat on the southern frontline against Sun Jian's forces drove Emperor Xian and later Dong Zhuo himself west to Chang'an in May 191.

Dong Zhuo once again demonstrated his political shortcomings by forcing millions of residents of Luoyang to migrate to Chang'an. He then set fire to Luoyang, preventing occupation by his enemies and destroying the biggest city in China at that time. In addition, he ordered his army to slaughter a whole village of civilians. The soldiers beheaded the civilians and carried their heads into Chang'an to show off as war trophies, pretending to have had a great victory against his enemies. A year later Dong Zhuo was killed in a coup d'etat by Wang Yun and Lü Bu.

In the same year, Emperor Ling died, and another struggle began between the court eunuchs for control of the imperial family. Court eunuchJian Shuo planned to kill General-in-Chief He Jin, a relative of the imperial family, and to replace the crown prince Liu Bian with his younger brother Liu Xie, the Prince of Chenliu (in present-day Kaifeng), though his plan was unsuccessful. Liu Bian took the Han throne as Emperor Shao, and He Jin plotted with warlord Yuan Shao to assassinate the Ten Attendants, a clique of ten eunuchs led by Zhang Rang who controlled much of the imperial court. He Jin also ordered Dong Zhuo, the frontier general in Liang Province, and Ding Yuan, Inspector of Bing Province^[7], to bring troops to the capital to reinforce his position of authority. The eunuchs learned of He Jin's plot, and had him assassinated before Dong Zhuo reached the capital Luoyang. When Yuan Shao's troops reached Luoyang, they stormed the palace complex, killing the Ten Attendants and 2,000 of the eunuchs' supporters. Though this move effectively ended the century-long feud between the eunuchs and the imperial family, it ushered in the era of warlords and martial law that became the Three Kingdoms era.

This event prompted the invitation of Dong Zhuo to enter Luoyang from the northwest boundary of China. At the time China faced the Qiang tribes in the northwest, and thus Dong Zhuo controlled a large army with elite training. When he brought the army to Luoyang, he was able to easily overpower the existing armies of both sides and took control of the imperial court, ushering in a period of civil war across China.

Dong Zhuo then manipulated the succession so that Liu Xie could take the throne in lieu of Liu Bian. Dong Zhuo, while ambitious, genuinely wished for a more capable emperor. On his way to Luoyang, he encountered a small band of soldiers protecting Liu Bian and Liu Xie fleeing the war zone. In the encounter Dong Zhuo acted arrogantly and threateningly, causing Liu Bian to be paralyzed with fear; Liu Xie, the future Emperor Xian, responded calmly with authority and commanded Dong Zhuo to protect the royal family with his army to return to the imperial court.

 Emperor Ling dispatched generals Huangfu Song, Lu Zhi, and Zhu Jun to lead the Han armies against the rebels, and decreed that local governments had to supply soldiers to assist in their efforts. It is at this point that the historical novelRomance of the Three Kingdoms begins its narrative. The Yellow Turbans were ultimately defeated and its surviving followers dispersed throughout China, but due to the turbulent situation throughout the empire, many were able to survive as bandits in mountainous areas, thus continuing their ability to contribute to the turmoil of the era.

The power of the Eastern Han Dynasty went into depression and steadily declined after the reign ofEmperor He from a variety of political and economic problems. A series of Han emperors ascended the throne while still youths, and de facto imperial power often rested with the emperors' older relatives. As these relatives occasionally were loath to give up their influence, emperors would, upon reaching maturity, be forced to rely on political alliances with senior officials and eunuchs to achieve control of the government. Political posturing and infighting between imperial relatives and eunuch officials was a constant problem in Chinese government at the time. During the reigns of Emperor Huan and Emperor Ling, leading officials' dissatisfaction with the eunuchs' usurpations of power reached a peak, and many began to openly protest against them. The first and second protests met with failure, and the court eunuchs persuaded the emperor to execute many of the protesting scholars. Some local rulers seized the opportunity to exert despotic control over their lands and citizens, since many feared to speak out in the oppressive political climate. Emperors Huan and Ling's reigns were recorded as particularly dark periods of Han Dynasty rule. In addition to political oppression and mismanagement, China experienced a number of natural disasters during this period, and local rebellions sprung up throughout the country.

In the second month of 184, Zhang Jiao, leader of the Way of Supreme Peace, a Taoist movement, along with his two brothers Zhang Liang and Zhang Bao, led the movement's followers in a rebellion against the government that was called the Yellow Turban Rebellion. Their movement quickly attracted followers and soon numbered several hundred thousands and received support from many parts of China. They had 36 bases throughout China, with large bases having 10,000 or more followers and minor bases having 6,000 to 7,000, similar to Han armies. Their motto was