This is the inevitable reason. All the above areas are located near 30 north latitude and have a climate suitable for the development of civilization. In the early days of human civilization, the ability to transform nature was still very low, mainly relying on natural resources. The basin is rich in water resources and fertile land, which is conducive to population growth. When the population of a region grows to a certain extent, it will naturally produce a detailed social division of labor, and then produce civilization.