Qin development immigrants

(1) The relationship between Qin and Han Dynasties and Xiongnu: The Qin Dynasty sent Meng Tian to attack Xiongnu in the north and recapture the Hetao area; The Great Wall of Wan Li was built to prevent Huns from harassing and plundering south. After the Battle of Pingcheng Deng Bai, Emperor Gaozu pursued a pro-Xiongnu policy. During the reign of Emperor Wu of the Han Dynasty, he launched three large-scale wars against the Xiongnu, thus relieving the Xiongnu's threat to the northern border counties of the Western Han Dynasty and all ethnic groups in the western regions. Since then, all ethnic groups in the western regions have been subordinate to the central government. In the Eastern Han Dynasty, the southern Xiongnu joined the Han Dynasty; In order to relieve the threat of the northern Xiongnu to all ethnic groups in the western regions, the northern Xiongnu was used twice to fight, and the northern Xiongnu was defeated and moved westward. The links between the mainland and the ethnic groups in the western region are increasingly close. (2) The effective jurisdiction of the Qin and Han Dynasties over the border areas. After the southern conquest of the Yue nationality in the Qin Dynasty, Guilin, Nanhai and Xiang Jun were established in the Yue nationality area. After the Northern Expedition of the Xiongnu in the Western Han Dynasty, the Western Regions Duhu was established in 60 BC. When Emperor Wu of the Han Dynasty set up a county in the southwest. During this period, the territory of a unified multi-ethnic country has been expanded. (3) Frontier development in Qin and Han Dynasties. The Qin dynasty immigrated to Hetao and Yue areas, and spread iron and technology to these areas. In the Han Dynasty, smelting, casting and sinking techniques were introduced to the Western Regions.