From the Eastern Han Dynasty to the Western Jin Dynasty, a large number of northern ethnic groups migrated inward. The main reason for this phenomenon is

According to meteorological research, from the first century AD to 600 AD, China's climate entered a cold cycle, reaching its peak around 400 AD. During this period, natural disasters were frequent across the East Asian continent. Cold and drought were accompanied by locust plagues. People in the Central Plains were in dire straits and starved to death everywhere. During the Western Jin Dynasty, a rare "tide of refugees" appeared in history. Groups of refugees in the north ignored the government's efforts to stop them. North China, northwest China and other places flocked to the warm and humid Jianghuai, Jiangnan, Sichuan and other places, and as far away as Lingnan. There were no less than 300,000 households recorded in history books alone, accounting for one-twelfth of the national household registration at that time. Even if this is the case in the Central Plains, it is not difficult to imagine what the situation is like in the Saibei grassland, which has a more fragile ecological environment. As early as the early Eastern Han Dynasty, the Xiongnu had already experienced "successive droughts, locusts, thousands of miles of bare land, withered grass and trees, famine and epidemics of humans and animals, and more than half of them died." "The tragic situation. Forced by various natural disasters, northern nomads have migrated southward into the North China Plain and the Yellow River Basin. Although the natural conditions here are not as good as those in the south, they are considered a paradise compared to their cold and barren hometown.