The Rise of Cao Cao

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 the Yellow river against Gongsun Zan, who held the northern frontier. Cáo Cāo, directly to Yuan's south, was engaged in a struggle against Yuan Shu and Liu Biao, who occupied respectively the Huai River basin and Middle Yang Zi regions. Further south the young warlord Sun Ce, taking over after the untimely death of Sun Jian, was establishing his rule in the Lower Yangzi, albeit as a subordinate of Yuan Shu. In the west, Liu Zhang held Yizhou province while Hanzhong and the northwest were controlled by a motley collection of smaller warlords such as Ma Teng of Xiliang, the original post of Dong Zhuo.
Dong Zhuo, confident in his success, was slain by his own adopted son, Lu Bu and his father-in-law Wang Yun. Lü Bu, in turn, was attacked by Dong Zhuo's supporters: Li Jue, Guo Si , Zhang Ji and Fan Chou. Wang Yun and his whole family were executed. Lu fled to Zhang Yan, 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.

 Modern Potrait of Cao Cao

Cao Cao, whose zone of control was the precursor to the Kingdom of Wei, had raised an army in the winter of 189. In several strategic movements and battles, he controlled the Dui 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 Turbans 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 Xuzhou, whose officers had executed his whole family. 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 Xuzhou entirely. However, Cao Cao received word that Lu Bu had seized Yan province in Cao Cao's absence, and accordingly he retreated, putting a halt to hostilities with Tao Qian for the time being. Tao Qian died that same year, leaving his province to Liu Bei. A year later, in 195, Cao Cao managed to drive Lü Bu out of Yan. Lu Bu fled to Xuzhou and was received by Liu Bei, and an uneasy alliance began between the two.
In the south, Sun Ce, then an independent general under the service of Yuan Shu, defeated the warlords of Yangzhou, including Liu Yao, Wang Liang, and Yan Baihu. The speed with which Sun Ce accomplished his conquests led to his nickname, "Little Conqueror" (小霸王), a reference to the late Xiang Yu. 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 Xuzhou, forming an alliance with Yuan Shu's remnant forces. Liu Bei and his two brothers, 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 Xia Pi. Lü Bu's officers deserted him, Yuan Shu's forces never arrived as reinforcements, and he was bound by his own officers Song Xian and Wei Xu and executed along with many of his officers. Thus, the man known as the mightiest warrior in the land was no more.
In 200, Dong Cheng, an officer of the Imperial Court, received a secret edict from the Emperor 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 co-conspirators executed, with only Liu Bei surviving and fleeing too Yuan Shao in the north.

Modern Potrait of Yuan Shao

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 Shaxian 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 met in force at GuanDu. Overcoming Yuan'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 Liu Biao of 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.