Why did the Han nationality in the Central Plains move to Jiangnan?

Mainly because of the war. The first migration of Han people from the Central Plains to the South began in the Qin Dynasty. Qin Shihuang developed Lingnan and set up a county against Vietnam. At that time, not only a large number of non-commissioned officers stayed in the south, but also a large number of people moved from the Central Plains to the south. The second time began in the late Eastern Han Dynasty. At that time, there was a long-term scuffle in the Central Plains, and a large number of people and gentry moved south (Zhuge Liang was one of them). The third time began in the late Tang Dynasty and the Southern and Northern Dynasties. At that time, the war in the north continued, ethnic minorities moved south, and a large number of Han people moved south. The fourth time began in the Song Dynasty, when the national strength was weak, and a large number of Han people and clans moved southward one after another to establish the Southern Song Dynasty. At this time, the economy of the south began to surpass that of the north. Later generations will be similar. There are many wars in the north and relative stability in the south, so the Han people in the Central Plains have moved to Jiangnan many times.