Why did the Han people in the Central Plains move south one after another?

After the collapse of the Western Jin Dynasty, various ethnic minorities competed to establish political power, and wars continued. The Han people in the Central Plains did not want to be ruled by the Hu people, so they moved south one after another. During the Western Jin Dynasty, the population of the northern states was about seven million. After the Yongjia Rebellion, 900,000 people crossed south many times, accounting for about one eighth. About five-sixths of the people in the Eastern Jin and Southern Dynasties were indigenous and one-sixth were overseas Chinese. Si Marui established a tacit understanding with the Wangs, a big family that closed the evil soul of the country. He went out of the south of the town and planned their retreat. As early as the first year of Yongjia (307), Si Marui had already left the town Jianye (later renamed Jiankang, now Nanjing, Jiangsu). After the fall of Chang 'an, in the first year of Jianwu (3 17), he was made King of Jin and ascended the throne the following year.