What are the bases in front of the Han Dynasty to resist the Huns?

Since Emperor Wudi personally visited the northern border, the strategy of the Han Dynasty towards the Xiongnu has been mainly to adopt the policy of frontal defense and weaken its aggressive forces until the second year of Emperor Xuan Di's reign (the first 6 years).

in 15 BC, the Hun Uwei Khan died, and his son Khan succeeded to the throne, so he moved his people and animals to the northwest for fear of being attacked by Han soldiers. Since then, his subordinates and the border counties corresponding to the Han Dynasty have also changed, with the left facing the clouds, the right facing Jiuquan and Dunhuang, and Khan's team facing Wuyuan to Jilusai. In response to this change, the Han Dynasty strengthened the management of Wuyuan and Shuofang, and built it into a forward base to resist the Huns. The main measures are as follows:

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(1) The Great Wall and city barriers along the border were added and repaired, and the legacy troops were constantly stationed. Guo Chang, a general who pulled Hu, was sent to promote the defense of Xiongnu in the area east of Tunshuo, Zhao Ponu, and ordered Guanglu to help Xu Zi build a city outside the Wuyuan Great Wall, starting from Guanglusai and building it all the way to Lugu in the northwest. After the completion of the project, the guerrilla general Han said that he would garrison these cities. He also ordered the crossbow general Lubod to repair tens of thousands of people to Juyansai (now the location of Ejina Banner). In Hexi Corridor, the Great Wall was built from Yongju (now Shuidengjing, Gansu Province) to Dunhuang, and a pavilion tunnel was built from Jiaohuang to Yanze (Luobnuoer), and other old Great Walls were also repaired on a large scale.

(2) Immigrants settle their fields. In the third year of Emperor Wudi's inaugural ceremony (the first 12 years), Shandong was flooded. Emperor Wudi moved the poor to the west of Hanguguan and more than 7, people in Qinzhong, south of Shuofang. In the sixth year of Yuan Ding (the first 111 years), he set up field officers in Shangjun, Shuofang, Xihe and Hexi, and ordered 6, frontier soldiers to station fields and defend the border. In the autumn of the first year of Tianhan (the first 1 years), we sent troops to garrison Wuyuan and the frontier, all of which were supplied by the government, and channels were dug in Shuofang and other places to divert water for irrigation, and tens of thousands of people were repaired. It can be seen that the scale of water conservancy projects at that time was quite magnificent. Therefore, from Wuyuan to Shuofang and then to Lingju in the west, according to historical records, farmland is adjacent and canals are staggered. There is no doubt that this area has been built into the main base to support the army to defend and go out.

(3) cut off the left and right arms of the Huns. On the eastern front, the Han Dynasty conquered Korea and Wuhuan, moved the people of Wuhuan to live in the northern part of Hebei and Zhaowudamang in Inner Mongolia, and ordered them to spy on the Huns. On the western front, Zhang Qian was sent to the western regions to marry the princess to King Wusun, and Li Guangli, the general of the Second Division, was sent to the west to attack Dawan and thirty-six countries. Four counties were set up in Hexi corridor, which isolated the connection between Xiongnu and Qiang.

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After a series of military, political, frontier defense and economic measures, the threat of Xiongnu slave owners was basically relieved. Xiongnu Khan repeatedly expressed his willingness to resume the pro-marriage, but Emperor Wu refused to agree and asked Xiongnu to surrender. As a result, the two sides remained hostile for a period of time. In the later period of Emperor Wu of the Han Dynasty, he sent troops to war for five times, most of which started from Wuyuan, Shuofang and Juyan. In the second year of Tai Chu (the first 13 years), Zhao Ponu rode more than 2, miles north of Shuofang with a rate of 2,, and the whole army was wiped out. In the second year of Tianhan (the first 99 years), Li Guang, the general of the Second Division, rode out of Jiuquan at an interest rate of 2,, and Li Ling took 5, soldiers out of Juyan to attack the Huns. Li Ling was defeated and surrendered. In the third year (the first 9 years), Li Guangli, the general of the Second Division, rode 7, troops out of Wuyuan, and two armies went out of Xihe (probably Jilusai), Jiuquan and other places, and went deep into Mobei to pursue the Huns. As a result, he was defeated again and Li Guangli surrendered.

why did emperor wudi send troops to mobei in his later period to pursue the Huns, often in vain, or even lost his master? The main reason is that the Huns felt that their strength could no longer compete with the Han Dynasty, so they moved to the northwest and avoided the front of the Han army. When the Han army was exhausted after a long journey, it seized the favorable opportunity and concentrated its efforts to attack the Han army all the way. Therefore, the Han army went out five times, either not seeing the enemy, or its troops were wiped out all the way.

at the end of emperor wudi's reign, he began to realize that soldiers and army horses suffered heavy casualties due to frequent use of troops. As a result, the people were overworked, the wealth was exhausted, the world was wasted, the people were displaced, and the peasant uprisings in various pools surged, so they had to stop using troops against the Huns.

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In the era of Emperor Zhaodi and Xuan Di, the Han Dynasty learned the experience and lessons of the late Emperor Wudi's use of troops, and adopted the policy of strategic defense. Instead of sending troops to attack, it only sent large armies to camp the nine capitals on the border for many times, and mainly strengthened the line from Wuyuan to Juyan. The Great Wall Pavilion Castle in Bianjun County is juxtaposed, and the bonfire is waiting to be smart. Therefore, during this period, the Xiongnu bandits stole less and less borders and captured less and less, and sometimes suffered heavy losses. They are like frightened birds. For example, in the second year of Xuandi Festival (the first 68 years), the imaginary right canal Khan was prepared to be close to Han, while the left big canal (the official name of Xiongnu) disagreed, and advocated sending troops to the border first to have a look. He volunteered to go south with King Hulu and 1, cavalry each. Walk to the road. Three people ran to the Han Dynasty to report the news, and Zuo Daqi quickly withdrew his troops. During this period, Huns Khan actively advocated reconciliation with Han, rarely violated the border, and dared not send people to the south to graze. They were afraid of the attack of the Han army, sent cavalry to defend the surrendered city, and built a bridge over my water to escape when the Han army attacked.

At this time, the Xiongnu became even weaker. Even the countries in the western regions and Ding Ling, Wu Huan and other ethnic groups sent troops to attack the Xiongnu. The nobles of many tribes in Xiongnu led their troops to surrender to Han due to the development of internal struggles among the ruling class.