Dong Zhou's death left a vacuum of power in the capital. Eventually, Cao Cao assumed the role of "protector" of the emperor. Cao Cao proved a capable leader, rewarding his men handsomely and attracting many fine generals and wise advisors to his administration.

Cao Cao also fought many battles against Liu Bei, who had shifted alliances, and Lu Bu. He eventually captured Lu Bu and had him executed. Liu Bei, however, proved more elusive.

When Liu Bei's oath-brother Guan Yu was captured during one of the battles, Cao Cao spared his life. He showered the captive with honors and gifts, including the famous horse, Red Hare, hoping to persuade Guan Yu to serve him. Guan Yu, however, was steadfast in his devotion to his oath-brothers, and Cao Cao couldn't help but admire him for it.

Soon, Guan Yu received word that Liu Bei was nearby. He escaped Cao Cao's camp and rode over 1,000 li (over 300 miles) to be reunited with his brother, killing six of Cao Cao's generals who blocked his way.

By now Cao Cao also had a strong enemy to his east: Yuan Shao. Yuan Shao had amassed an army of 700,000 and was preparing to march on the capitol. Cao Cao brought out a force of only 70,000 to fight him. Mostly due to his own indecisiveness, Yuan Shao lost a key battle at Guandu. Cao Cao soon secured northeastern China and laid the foundation for the Wei kingdom.