This is when Li Tangshan and Panli rushed to Yangshan, Xianyang City came to the north of the Xiongnu to invade the border, Qin Shi Huang sent the general Meng Tian to lead 300,000 troops to attack the Xiongnu in the north, Meng Tian's army captured Henan (now Inner Mongolia, Hetao area), occupied Yangshan (today's Wolf Mountain in Inner Mongolia Urad Houqi), set up Jiuyuan County (now Mengjiawan in the northwest of Baotou, Inner Mongolia), and the Great Wall originally built by Qin, Yan and Zhao was added and repaired, and the Great Wall of Lintao in the west and Liaodong in the east was established. It has become a fortress for the Han people in the Central Plains to resist the northern nomads for thousands of years.

On the vast map of Great Qin, there is such a people, they like to fight on horseback, we call them "Xiongnu". In the struggle for power and profit among the ruling layers, the Southern Xiongnu became independent and participated in the melee in the Central Plains. It also had to go north to the Xiongnu to fight the invading external forces. And which force can take the lead in completing the nine attacks on the Xiongnu will become a symbol of the strength and honor of the force.

Most of the Xiongnu lived in the Gobi Desert, and the weather conditions were bad, and in the process of the Northern Expedition against the Xiongnu, the weather conditions were the key to victory. Especially in sandstorms, there will be hurricanes, and longbowmen will not be able to go into battle due to strong winds; When an earthquake occurs, there is a danger of landslides and ground cracks, and the attack of the trap soldiers will be limited. Of course, they can also use the weather skillfully to defeat the strong, especially in the blizzard, the defense of the heavy shield will be greatly improved, providing stronger protection for the troops.

In the process of the Northern Expedition to the Xiongnu, the strategy is not limited to the understanding of generals and troops, but also the selection of the most favorable lineup for the environment.

In the spring of the 33rd year, the main army of Meng Tiantong went north from Shangjun (County Zhifushi, now south of Yulin City, Shaanxi) to attack the east of the Great Wall; Yang Wengzi led his division from Xiaoguan (now southeast of Guyuan, Ningxia) out of the Great Wall to attack its west. The Huns were defeated and fled. Qin then took Henan (south of the Wujia River in present-day Inner Mongolia and the land of the Yikezhao League). 44 counties were placed along the river, and immigrants were reclaimed. Due to the continuous attack of the Xiongnu, in the autumn of the following year, Qin Shi Huang reinstated the Meng Tian army to cross the Yellow River to the north, take Gaoque (now Jilan Pass in the middle of Wolf Mountain, Inner Mongolia), and capture Yangshan (now Wolf Mountain and Yin Mountain in the north of Wujia River in Inner Mongolia) and Beijiao (now the area of Jiashan and River in the south of Wujia River). The Xiongnu were defeated and migrated north. In order to consolidate the Henan region, Qin placed Jiuyuan County (郡治九原, northwest of present-day Baotou City, Inner Mongolia). In order to prevent the Xiongnu from moving south, Meng Tian was ordered to recruit a large number of migrant workers to build the Great Wall from Lintao (now Minxian County, Gansu) in the west to Liaodong in the east on the basis of the Great Wall of Yan, Zhao and Qin, which played an important role in consolidating the borderland in northern Qin.

The Xiongnu are one of the nomadic people living in northern China, and have long been active between the Yin Mountains in the south and Lake Baikal in the north, becoming a powerful nomadic people in the north.

In the late Warring States period, the Xiongnu had entered a slave society. Slave-owning nobles took advantage of the swift movement of cavalry and often penetrated deep into the Central Plains to harass and plunder the inland tribes, which were mainly agricultural. At that time, Qin, Zhao, and Yan were neighbors with the Xiongnu, and wars often broke out. As the countries were busy with civil wars, they generally took a defensive position against the Xiongnu, building the Great Wall in the north and sending troops to defend it. After the unification of Qin, the Xiongnu still posed a great threat to Qin.

Such a populous ethnic group is bound to pose a considerable threat to the newly established Qin Dynasty. This kind of threat is unavoidable for the ambitious and high-spirited iron-blooded Qin Shi Huang and the entire Qin Empire, and if the empire is to remain strong and strong, it is necessary to strike at external threats.

As a result, the Qin Empire's conquest of the Xiongnu inevitably occurred. The Central Plains were chaotic, and the Qin State was busy unifying the six countries, and each country did not have the energy to deal with the Xiongnu in the north, and the Xiongnu took the opportunity to move south, reoccupy many parts of the northern border counties, and used Henan (present-day Inner Mongolia and Hetao regions) as a stronghold, directly threatening Xianyang, the political center of the Qin Dynasty. The use of troops against the Xiongnu and the elimination of the military threat of the Xiongnu became a top priority after the Qin Dynasty unified the six countries.

On the one hand, he appointed Meng Tian as the commander-in-chief, led the troops to garrison Shangjun (County Zhifushi, now southeast of Yulin, Shaanxi), long-term management of the northern frontier, guarding the safety of the Qin capital Xianyang, Meng Tian began to guard the border for more than ten years, and had a good understanding of the mountains and rivers in the north, and prepared for the future counterattack against the Xiongnu, on the other hand, the first emperor ordered the repair of the Great Wall, the border between the Qin Dynasty and the Xiongnu and other northern minorities was as long as 10,000 miles, and it was unrealistic to send troops everywhere to defend the garrison, and the Xiongnu were mainly cavalry, Strong mobility, fast movement, in order to better defend the Huns southward, the Qin Dynasty set the defense policy of defending against cavalry with walls, and ordered the comprehensive repair of the Great Wall built by the original Qin, Zhao and Yan, and connected them to form a Great Wall from Lintao in the west to Liaodong in the east.

Li Tangshan and Yan Le agreed to arrive 7 days earlier. Li Tangshan decided to go to Li Xin and them first, he hadn't seen this little brother since the southern expedition, and he still missed them very much.

Li Tangshan arrived at Jiuyuan County (Bayannur), where Li Xin's troops were stationed. The Hetao irrigation area in Bayannur is the largest artesian irrigation area in Asia, and the Hetao Plain in the territory has the reputation of "plugging the south of the Yangtze River". Patches of colorful wildflowers dot the grassland, like a large colorful carpet. The reckless wilderness exudes a fresh, damp earthy scent.

Li Tangshan and Li Xin have not seen each other for many years, Li Xin is very grateful to Li Tangshan in his heart, without Li Tangshan's help, Li Xin may never have a comeback.

Li Xin gave Li Tangshan a privilege in Jiuyuan County, where he could pass at will.

In the north of Yinshan Mountain, where the Xiongnu are active, Bayannur is a large plain behind it.

On the grassland, the yurts are dotted, the smoke curls, the sheep shine, and the horses neigh. The scenery of the grassland, the melodious sound of the horse-head qin, the fragrant milk tea, the simple and high-pitched Mongolian folk songs, and the hospitable Mongolian compatriots...... The horses are galloping, the herdsmen are singing, and the small flowers, cattle and sheep, horses, and shepherds on the grassland constitute a very beautiful picture.

Li Tangshan remembered a folk song of the Northern Dynasties: "The sky is vast, and the wilderness is vast." The wind blows the grass and sees the cattle and sheep low. "It's a true portrayal of the beautiful scenery in front of you.

At this time, Li Tangshan understood from Li Xin's mouth that Yangshan was relative to Yinshan, and the westernmost section of Yinshan was "Yangshan". That is, the wolf mountain of the Urad Houqi in Inner Mongolia. It traverses more than 100 kilometers in the south of the Urad Houqi, with mountain peaks towering, steep in the south and gentle in the north. The banner is a unique county-level administrative region of the Inner Mongolia Autonomous Region, that is, the administrative status is the same as that of the county. Wuhou Banner is located in the middle temperate zone, belongs to the plateau continental climate, the main characteristics are: cold and dry in winter, more wind and sand, less drought and rainfall in summer, strong sunshine, and large evaporation.