In ancient China,Guo referred to city or state.Zhonguo (now it means China) meant the central city or the central state. According to historical books, Zhongguo had five connotations: fist, the capital city; second, the state ruled by the emperor; third, the Central Plains; fourth, the upland region and last, the region dwelled by Han and Xia nationalities.
Since the Han Dynasty (206BC-220AD), people often referred the state established by the Han nationality as Zhongguo; however, other nationalities also call their own states as Zhongguo. Neither of them would acknowledge other Zhongguo.
Strictly speaking, Zhongguo in ancient times was an adjective rather than a proper noun. None reigning dynasties tookZhongguoas their name, and they all had their own titles.
After the 1911 Revolution (the Chinese bourgeois democratic revolution led by Dr. Sun Yat-sen which overthrew the Qing Dynasty), Zhongguo was taken as the shortened form of Republic of China. And in 1949, Zhongguo became the shortened form of the People's Republic of China.
Now, the only one Zhongguo in the world is thePeople's Republic of China with its capital in Beijing.