1. External reasons: In ancient times, due to time and geography, the ground combat power has been very developed, and every war in ancient times also started from the north. From Qin and Han Dynasties to Tang and Song Dynasties, the Song Dynasty moved its capital to Jiangnan, laying the foundation for modern Jiangnan to become a rich land. The Yangtze River, which causes the fertility difference between the north and south alluvial plains, is also a natural barrier since ancient times: Jiangnan is fertile and less disturbed by the northern nationalities, and it has jumped from the stage of "survival" to the stage of "development", which has made Jiangnan an open-minded and culturally developed personality; Jiangbei, on the other hand, often struggles on the "survival line". From Wei, Jin, Tang and Song Dynasties to Ming and Qing Dynasties, there were frequent wars, which also caused Jiangbei to be complacent.

2. Imperial reasons: Jiangnan, with its geographical convenience and cultural closeness, allows scholars in Jiangnan to study with peace of mind. However, due to the war in Jiangbei, life has become a problem, so most of the scholars in Jiangbei are military commanders, while those in Jiangnan are better at imperial examinations. Since ancient times, military commanders have founded the country and civilian officials have ruled the country. When it is stabilized and the rights of civil servants are increased, they will feed their own Jiangnan and make the land of Jiangnan prosperous.

3. Economic reasons: Since the Ming and Qing Dynasties, some handicraft departments in the south of the Yangtze River have had capital production relations, that is, employment relations. It is embodied in three aspects: first, in Suzhou and Hangzhou, the center of silk weaving industry, machinists are employed by machinists; Second, in Songjiang, the center of cotton textile industry, manufacturers employ residents; Third, there is also an employment relationship in ironmaking in Guangdong. As a result, Jiangnan's economy has soared, and Jiangbei is far behind.

4, weather reasons: Since ancient times, there has been a saying that floods are a front line and droughts are more than half. Due to geographical reasons, the north often suffers from drought and the land is not harvested; The flood disaster in the south will only affect the residents on both sides of the Yangtze River basin, but has little impact on the entire southern economy, so it is easier to recover.

5. Other reasons: In the late Ming and early Qing dynasties, trading ports began to open. Although they were troubled by Japanese pirates during this period, the impact on the overall economic development was negligible. Foreign trade brings real money and silver, which is also an important reason for the prosperity of the whole south of the Yangtze River.