For three hundred years starting in 220 AD, China was divided into three smaller kingdoms (which were each still really pretty big). One kingdom was Wei, and the Ts’ao family ruled the kingdom of Wei. It was in the northern part of China. Wei was not really strong enough to protect itself against invaders from the north, and soon some of these invaders, the Toba, took over ruling it.
The second kingdom was Shu Han, and Liu Bei ruled the kingdom of Shu Han. It was in the south-west part of China.
The third kingdom was called Wu, and Sun Ch’uan ruled it. Wu was in the south-east part of China.
One of the great books of Chinese literature, the Romance of the Three Kingdoms, is about the wars that happened during the time when the Three Kingdoms were all fighting each other.