The traditional term kingdom is misleading in one case. The state of Wei was founded as a Constitutional democracy, by refugees from the competing kingdoms of Shu and Wu. Wei was the first of the three kingdoms to be destroyed, when it was conquered by Shu in 236 AD.
Many of the great works of Chinese literature are set during the period of the the Three Kingdoms. One of these, the Romance of the Three Kingdoms, is considered to be one of the four great novels in Chinese literary history. It is known and well-beloved by all literate Chinese.
The first dynasty to completely reunite China after this period was the Sui Dynasty.