Han–Xiongnu Wars
The Han–Xiongnu Wars or Sino-Xiongnu Wars, were a series of military conflicts fought from 133 BC to 89 AD between the agrarian Chinese Han Empire and the nomadic Xiongnu confederacy, although extended conflicts can be traced back as early as 200 BC and as late as 188 AD.
The Chinese civilization initially clashed with Inner Asian nomadic tribes that would later become the Xiongnu during the Warring States period, and various northern states built elongated fortifications to defend against raids down from the Mongolian Plateau. The unified Qin dynasty, who conquered all other states under Emperor Qin Shi Huang, dispatched General Meng Tian in 215 BC in a successful campaign to expel the Xiongnu from the Ordos region. However, the subsequent civil wars following the Qin dynasty's collapse gave the Xiongnu tribes, who were then unified into a large confederacy under Modu Chanyu, the opportunity to reinvade the Ordos region. After the Han dynasty was established in 202 BC, Emperor Gao tried to fight off Xiongnu invasions but had himself trapped in an ambush during the Battle of Baideng, and a truce was negotiated by bribing Modu's wife, thus ending first Han–Xiongnu War. Decades of de jure peace then followed with the Chinese gifting "harmony via marriage" to appease the Xiongnu, who still routinely raided Chinese borderlands.
However, starting from the reign of the seventh Han ruler, Emperor Wu, the foreign policy of the Han Empire began to change from bring relatively passive to using a proactive strategy seeking to permanently remove the northern threat. The tension fully escalated in 133 BC when the Han army unsuccessfully tried to ambush Xiongnu raiders at Mayi, and retaliatory raids intensified. Emperor Wu then started deploying newer generations of offensive military commanders such as Wei Qing and Huo Qubing, and launched several victorious expeditions to control the Ordos Loop, Hexi Corridor and Western Regions, eventually pushing the Xiongnu north beyond the Gobi Desert with a decisive campaign in 119 BC. After the death of Emperor Wu in 87 BC, the conflict de-escalated to mostly small border conflicts, although Emperor Xuan and Yuan each sanctioned major offensives against the Xiongnu during their reigns. The overall strategic Han successes against the Xiongnu allowed the Chinese to project their influence deep into Central Asia, which eventually led to the establishment of a regional protectorate in 60 BC. For the Xiongnu, the situation deteriorated with each setback, leading to erosion of the Chanyu's prestige among the steppe tribes, and the subsequent internal power struggles further weakened the nomadic confederacy, fracturing it into various self-ruling factions. The Han Empire then adhered to a divide and rule strategy, using marriage alliances to recruit some against others.
During the interregnum Xin dynasty, Wuzhuliu Chanyu waged war in 11 AD after Wang Mang, a consort kin who usurped the Western Han throne, attempted to split the Xiongnu by installing 15 new chanyu. Wang Mang mobilized 300,000 troops against Xiongnu and forced Goguryeo, Wuhuan and various Western Regions city-states to send conscripts and provisions, which led to the mass defection of these vassal states. After the Eastern Han dynasty was established in 25 AD, the Chinese initially found their hands full after the chaotic civil war and could not afford any full-scale mobilizations against the Xiongnu raids, they therefore resorted to continue lobbying amongst Xiongnu faction rulers instead. This continued for another two decades until 46 AD, when repeated natural disasters severely weakened the Xiongnu and forced them to flee north from an attack by Wuhuan. The Xiongnu then permanently split into two groups in 48 AD, becoming the Northern and Southern Xiongnu. The Southern Xiongnu submitted as vassals to the Han Empire, and served as auxiliaries in Han wars against the Northern Xiongnu and other hostile Donghu states like the Xianbei. The Northern Xiongnu continued to resist the Han and were eventually evicted westwards by further Han expeditions. In 89 AD, General Dou Xian led 50,000 cavalry on an expedition that decisively defeated the Northern Xiongnu's main force, causing it to split further. In 91 AD, Northern Chanyu was defeated in the Battle of the Altai Mountains, and they fled west into Dzungaria, where they continued causing sporadic troubles until 151 AD when a 4,000-strong Han militia was enough to defeat them, causing them to flee further west into Central Asia where they disappeared from historical records. The Southern Xiongnu continued to be vassals of the Eastern Han dynasty, though they occasionally launched revolts until as late as the Yellow Turban Rebellion era. Nonetheless by 89 AD onwards the Han Empire's main concern had already switched to the Qiang people, who had become a bigger threat than the Xiongnu.
Background
During the Warring States period, the Qin, Zhao, and Yan states conquered various nomadic territories inhabited by the Xiongnu and other Hu peoples. They strengthened 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 China proper. 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 of expanding his empire. Later that year, 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 and General Meng Tian were stationed at a garrison in Suide and soon began the construction of walled defences, connecting them 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.However, after the sudden death of Qin Shi Huang, the ensuing political corruption and chaos during the short reign of Qin Er Shi led to various anti-Qin rebellions, eventually brought about the collapse of the Qin dynasty. A massive civil war then erupted between various reinstated states, with Liu Bang eventually being victorious and establishing the Han dynasty. During the transitional years between Qin and Han, while the Chinese were mainly focused towards the interior of their nation, the Xiongnu took the opportunity to retake the territory north of the wall. The Xiongnu frequently led incursions to the Han frontier and had considerable political influence over the border regions. In response, Emperor Gaozu led a Han army against the Xiongnu in 200 BC, pursuing them as far as Pingcheng before being ambushed by Modu Chanyu's cavalry. His encampment was encircled by the Xiongnu, but Emperor Gaozu escaped after seven days. After realizing that a military solution was not feasible for the time being, Emperor Gaozu sent Liu Jing to negotiate peace with Modu Chanyu. In 198 BC, a marriage alliance was concluded between the Han and the Xiongnu, but this proved far from effective as the incursions in the frontier regions continued.
Course
Onset
By the reign of Emperor Wu, the Han empire was prospering and the national treasury had accumulated large surpluses. However, burdened by the frequent Xiongnu raids on the frontier, the emperor abandoned the policies of his predecessors of maintaining peace with the Xiongnu early in his reign. In 136 BC, after continued Xiongnu incursions near the northern frontier, Emperor Wu had a court conference assembled. The faction supporting war against the Xiongnu was able to sway the majority opinion by making a compromise for those worried about stretching financial resources on an indefinite campaign: in an engagement along the border near Mayi, Han forces would lure Junchen Chanyu over with wealth and promises of defections to eliminate him and cause political chaos for the Xiongnu. Emperor Wu launched his military campaigns against the Xiongnu in 133 BC.In 133 BC, the Xiongnu forces led by the Chanyu were lured into a trap at Mayi, while a Han army of about 300,000 troops laid in ambush against the Xiongnu. Wang Hui led this campaign and commanded a force of 30,000 men strong, advancing from Dai with the intention of attacking the Xiongnu supply route. Han Anguo and Gongsun He commanded the remaining forces and advanced towards Mayi. Junchen Chanyu led his army of 100,000 men towards Mayi, but he became increasingly suspicious of the situation. When the ambush failed, because Junchen Chanyu realized he was about to fall into a trap and fled back north, the peace was broken and the Han court resolved to engage in full-scale war. In light of this battle, the Xiongnu became aware of the Han court's intentions to go to war. By that point the Han empire was long consolidated politically, militarily, and economically, and was led by an increasingly pro-war faction in the imperial court.