Since the end of the Eastern Han Dynasty, due to the increasingly serious political corruption, the unified multi-ethnic empire has fallen apart. After that, the brief unification of the three countries and the Western Jin Dynasty led to the coexistence of sixteen countries in the Eastern Jin Dynasty and the confrontation between the Northern and Southern Dynasties. In more than 300 years of political division and frequent wars, China society is in a huge turbulent vortex. At the same time, due to the great migration and mixed ethnic groups, the unprecedented second great ethnic integration took place in the history of China.
During this period, all ethnic groups closely related to the Han nationality and its predecessor, Huaxia nationality, suddenly accelerated the process of ethnic integration after they entered the political arena of the Central Plains, and they dispersed in succession. Many ethnic groups that have established political power have merged with the Han nationality. Whether in the south or the north, the two-way or multi-directional migration and convection between ethnic groups are the characteristics of national integration in this period. That is, some Han people go to the surrounding areas, and the surrounding ethnic minorities come to the mainland.
In the north, ethnic groups such as Xiongnu, Xianbei, Jie, Shi and Qiang, known as the "Five Lakes" in history, came in droves and established many political powers in the Yellow River basin. Generally, no matter which ethnic group is in the dominant position, these ethnic regimes are mostly related to the clan class of the Han nationality; At the same time, the combination of political forces often takes various forms of alliances. Northern nationalities migrated to the Central Plains and established political power. One of the most direct consequences is that Hu and Han live together in the Central Plains, which provides a prerequisite for the integration of all ethnic groups. In the long-term coexistence and intermarriage with the Han nationality, these ethnic groups are interdependent, absorbing each other and establishing countless contacts. Gradually, the differences between them and the Han nationality in economy, culture, language, costumes, surnames, customs and even religious beliefs gradually narrowed and gradually merged with the Han nationality. For example, in the late Northern Wei Dynasty, ethnic minorities such as Xiongnu, Mangan, Shi and Qiang had disappeared from history, while Rouran, Tuguhun and Zile gradually merged with the Han nationality. By the time the Sui Dynasty unified the Yellow River basin, almost all the ethnic minorities who moved from the north to the Central Plains were integrated by the Han nationality, and even the Xianbei nationality finally completed the sinicization. Of course, under the background of national integration in this period, the important event that has to be mentioned is the reform of Emperor Xiaowen in the Northern Wei Dynasty.
In the south, since the Qin and Han Dynasties, many China people or Han people have entered the barbarian areas, southwest Yi and Lingnan areas in large numbers. During the Wei, Jin, Southern and Northern Dynasties, in order to escape the war and heavy taxes, the Han nationality moved to Longyou and Hexi, or moved to Jiangzuo with the Jin family moving south, even in traditional settlements such as barbarians, slang, Liao and Yi. At the same time, Yuzhou people, Man Jing people and Zhou Yong people moved northward, and these people were recruited to the mainland to become editors of the Southern Dynasties. Through this two-way, countercurrent migration and mixed habitation, as well as uninterrupted military conquest, marriage alliance and the establishment of Zuojun County, the phenomenon of Han alienation and Yi Sinicization has become more and more common in southern China.