Han–Xiongnu War
In 119 BC, when the Xiongnu suffered a catastrophic defeat by the Han armies, the Chanyu moved his court (located in present-day Inner Mongolia) to another location north. This had the desired result that the Xiongnu were separated the Wuhuan people, which also prevented the Xiongnu from exacting many resources from the Wuhuan. The Han court placed the Wuhuan in tributary protection and resettled them in five northeastern commandaries, namely Shanggu, Yuyang, Youbeiping (present-day Hebei), Liaoxi, and Liaodong (present-day Liaoning). A new office, the Colonel-Protector of the Wuhuan, was established (near present-day Beijing) in order to prevent contact between the Wuhuan with the Xiongnu and to use them to monitor the Xiongnu activities. Nevertheless, the effective Han control over the Wuhuan was lacking through much of the Western Han period, since the Xiongnu had considerable military and political influence over the Wuhuan while relations between the Wuhuan and Han often remained strained at best. This can be exemplified by a situation in 78 BC, when the Xiongnu led a punitive campaign against the Wuhuan, resulting in General Fan Mingyou (范明友) leading a Han army to impede further incursions. When they learned that the Xiongnu had left by the time the army arrived, the Han court ordered Fan to attack the Wuhuan instead, killing 6000 Wuhuan men and three chieftains, since the Wuhuan had recently raided Han territory. Only in 49 AD, when 922 Wuhuan chieftains submitted during Emperor Guangwu's reign, did many of the Wuhuan tribes come under tributary system of the Han empire. The Han court provided for the Wuhuan and in return the Wuhuan tribes guarded the Han frontier against the Xiongnu and other nomadic peoples.
Han–Xiongnu War
During the Warring States period, the Qin, Zhao, and Yan states conquered various nomadic territories inhabited by the Xiongnu and other Hu peoples. They strengthen their new frontiers with elongated wall fortifications. By 221 BC, the Qin ended the chaotic Eastern Zhou period by conquering all other states and unifying the entire nation. In 215 BC, Qin Shi Huang ordered General Meng Tian to set out against the Xiongnu tribes, situated in the Ordos region, and establish a frontier region at the Ordos Loop. Believing that the Xiongnu were a possible threat, the emperor launched a pre-emptive strike against the Xiongnu with the intention to expand his empire. Later that year (215 BC), General Meng Tian succeeded in defeating the Xiongnu and driving them from the Ordos region, seizing their territory as result. After the catastrophic defeat at the hands of Meng, Touman Chanyu and his followers fled far into the Mongolian Plateau. Fusu (Prince of Qin) and General Meng Tian were stationed at a garrison in Suide and soon began with the construction of the walled defenses, connecting it with the old walls built by Qin, Yan and Zhao states. The fortified walls ran from Liaodong to Lintao, thus enclosing the conquered Ordos region, safeguarding the Qin empire against the Xiongnu and other northern nomadic people. Due to the northward expansion, the threat that the Qin empire posed to the Xiongnu ultimately led to the state formation of the many tribes towards a confederacy.