In 22 1 BC, Qin Shihuang annexed six countries, and in the "great unification", the Chinese nation also moved from decentralization to unity. After Qin Shihuang established the Qin Dynasty, he took a series of measures to unify and stabilize the Chinese nation, such as implementing the county system, stipulating that "books should be written in the same language", unifying currency and weights and measures, "cars on the same track" and "walking along the same road", and building the Great Wall. For the first time in China's history, a unified autocratic and centralized feudal country was established. Under the condition of national unity, the Han nationality has formed a unified nation.
After the reunification of the Qin Dynasty, the Chinese family name was still used. People from Shandong (east of Lushan Mountain) who originally belonged to six countries were all "leaders of Guizhou" in the Qin Dynasty. Although the state of Qin was short-lived, the peoples from the Western Regions (including present-day Xinjiang) and the Xiongnu to the Han Dynasty were still called Qin people in the Central Plains. The Han Dynasty lasted more than 400 years from the Western Han Dynasty to the Eastern Han Dynasty, which provided historical conditions for the name of the Han Dynasty and the name of the Chinese nation.
In addition, the Han Dynasty was a powerful country. In foreign exchanges, other nationalities call the army of the Han Dynasty "Han soldiers", the envoys of the Han Dynasty "Han envoys" and the people of the Han Dynasty "Han people". Therefore, in the unprecedented frequent exchanges between the Han Dynasty and the surrounding ethnic minorities, such as communicating with the western regions, conquering the Xiongnu, pacifying the western Qiang, recruiting and surrendering North Korea, serving the southwest Yi, and incorporating Fujian and Nanyue, the name of the Han Dynasty was called the name of the Chinese nation by other ethnic groups. Lv Simian said: "The name of the Han nationality began after Liu Bang proclaimed himself emperor." ?
After the Eastern Han Dynasty, the Central Plains was in chaos, the centralized feudal country was divided, the feudal regime was divided, and disputes and wars were everywhere. During the great division, melee and turmoil, various ethnic groups or tribes migrated everywhere, and Xiongnu, Xianbei, Wuwan, Di and Qiang in the north entered the Central Plains one after another, which was called "five wild flowers" in history, and some barbarians in Jianghan area also poured into the Central Plains.
In the Central Plains, the Han people live together with Xiongnu, Xianbei, Wuwan, Di, Qiang and Barbarians. The Han people in the north moved south in large numbers; The Han nationality, known as "Nandu" in history, and southern minorities or tribes, such as barbarians, slang and Liao, live together in the Yangtze River and Pearl River basins. However, most of them have been assimilated by the Han nationality, lost their national characteristics and become a part of the Han nationality.
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On several occasions in history, the Han population migrated from the Yellow River basin and north of Huaihe River to the south of Yangtze River and Pearl River basin. When Qin unified the six countries, a large number of Kanto nobles moved to Guanzhong, and there were similar immigration activities in the Western Han Dynasty. However, the economic development at that time determined that the counties in the middle and lower reaches of the Yellow River were the most densely populated areas in China.
For example, if a county is divided into two parts, the northern part accounts for about 80% of the total registered population at that time, and the southern part accounts for about 20%. From the end of the Eastern Han Dynasty, people began to move south. By the end of the Western Jin Dynasty, people in the Yellow River basin moved south to the middle and lower reaches of the Yangtze River, the upper and middle reaches of the Yangtze River and the Hanshui River basin on a large scale.
After the Northern and Southern Dynasties, the population continued to move south, which made the population of the Yangtze River basin increase continuously, but it still did not change the situation that the population distribution in the north was more than that in the south. However, if the total population of southern counties in the late Sui Dynasty is compared with that in the Western Jin Dynasty, the population of the Yangtze River basin and Lingnan area has more than doubled.
In the late Tang Dynasty and the Five Dynasties, the northern population moved south again. At the end of the Northern Song Dynasty, Jin Bing committed crimes in the south, and there was a climax of the second population migration to the south. The population in the south has increased greatly, mainly concentrated in the Sichuan Basin and around Dongting Lake, Poyang Lake and Taihu Lake, as well as the Yangtze River and Pearl River Delta.
These places have become densely populated areas, and the population density is higher than that of the northern States. In addition to the above two large-scale population movements to the south, there are several other large-scale population movements to the south. The southern economy has developed rapidly since the Eastern Jin Dynasty. By the Song Dynasty, China's economic center of gravity had shifted to the south. By the Ming and Qing dynasties, the population density in the south was not only higher than that in the north, but also the total population of Han nationality exceeded that in the north.
After thousands of years of migration and migration with various nationalities in China, the Han nationality has formed the distribution characteristics of being concentrated in the most developed agricultural areas and cities in the Songliao Plain, the Yellow River, the Huaihe River, the Yangtze River and the Pearl River Basin, and interwoven with local ethnic groups in the border areas.
In the long historical development process, a considerable number of Han people emigrated overseas. Some of them took root in immigrant countries and became local Chinese, while others retained their China nationality and became overseas Chinese scattered around the world.