Ancient immigrants supported the border.

Analysis of test questions: (1) The reasons of population migration in the history of China, among which the most direct ones are immigration, war and natural disasters. For example, in the history of our country, every time there is a war or famine, it will cause a large-scale population migration. (2) The characteristics of population migration from the founding of New China to 1980s are small scale, low frequency, influenced by national policies, planned economy and strict household registration management. (3) Since the reform and opening up, China's population migration has become increasingly active, which is mainly manifested in the following aspects: the floating population has increased greatly and is spontaneous. From the flow direction: first, from rural areas to cities; Second, from inland provinces to coastal cities and industrial and mining areas.

Comments: This question is moderately difficult. In different periods of our country, the reasons for population migration are different.