After Dong lost, the emperor was in the clutches of his followers—until Cao Cao saved him and seized control over him. Cao Cao tried to conquer all of China for the emperor but in fact wanted to conquer it for himself. He defeated Liu Bei once at the Battle of Changban in 207 but was not able to win the Battle of Red Cliffs against the united forces of Liu Bei and Sun Quan, a warlord in the South.