At the end of the Eastern Han Dynasty (A.D. 184 Yellow Scarf Uprising) to the establishment of the Sui Dynasty (A.D. 58 1 year), only the Western Jin Dynasty was briefly unified. (AD 280-2 16), about 400 years. During this period, there was always chaos in the Northern Dynasties, and there were also ethnic minority regimes.

Another period was from the end of the Tang Dynasty (907) to the unification of the Yuan Dynasty (1276), which lasted about 400 years. Since the partial reunification of the Northern Song Dynasty, the Northern Song Dynasty began to coexist with western Liaoning and Xia, and then the Southern Song Dynasty rose, and Jin, Xixia and Mengyuan unified the whole country.

It is necessary to analyze the meaning of the problem in detail and find the starting point.