Battle of Mobei
[3][4][5][6] Military tension had for a long time existed in ancient China between Central Plain polities and the northern barbarians, mainly because the fertile lands of the prosperous agricultural civilization presented attractive targets for the militaristic nomadic tribes.
During the Zhou dynasty, northern vassal states such as Yan, Zhao and Qin resorted to defensive strategies, constructing elongated fortresses that served as the precursors of the Great Wall of China.
With the collapse of the Qin dynasty and the Chu-Han contention, the Xiongnu gained the opportunity to become unified under Modu Shanyu and quickly expanded into a powerful tribal confederacy that ruled over a vast territory across Central and East Asia.
When the Chu-Han contention concluded, Emperor Gao recognized the threat posed by its hostile northern neighbour and in 200 BC launched a massive campaign.
After the Han army was lured into an ambush and encircled by 300,000 elite Xiongnu cavalry for seven days, the siege was relieved only after messengers were sent to bribe the Shanyu's wife.
The "peaceful" atmosphere was broken in 133 BC after a large ambush operation was staged at Mayi but aborted after the Xiongnu discovered the trap and retreated.
Over the next ten years, Emperor Wu repeatedly deployed Wei and his vigorous nephew Huo Qubing against Xiongnu forces thus recapturing large areas of land and dealing devastating blows.
Evicted by the defeats, Yizhixie Chanyu (伊稚邪) took Zhao Xin's advice, and the Xiongnu tribes retreated to the north of the Gobi Desert, hoping that the barren land would serve as a natural barrier against Han offensives.
He then went on to conduct a series of rituals upon arrival at the Khentii Mountains (狼居胥山, and the more northern 姑衍山) in order to symbolize the historic Han victory, then continued his pursuit as far as Lake Baikal (瀚海), effectively annihilating the Xiongnu clan.
[3][4][5] A separate division led by Lu Bode (路博德), set off on a strategically flanking route from Right Beiping (右北平), joined forces with Huo after arriving in time with 2,800 enemy kills.
The Han forces killed over 19,000 enemies and pursued the remainder another 100 miles to the Khangai Mountains where they besieged then captured the Fortress of Zhao Xin located in the Orkhon Valley.
Li Guang, frustrated and humiliated as this was his last chance to obtain sufficient battle distinctions to receive a marquessate as a reward, committed suicide to preserve his honour.
Apart from loss of manpower due to wartime casualties and diseases, the nomadic Xiongnu lost millions of livestock, their vital food resource, to the Han army, and the war left a large proportion of the remaining cattle suffering miscarriages during their reproductive seasons.
[3][7] Furthermore, the loss of control over the fertile southern grassland meant that Xiongnu had to hole up in the cold, barren land of the northern Gobi Desert and Siberia, struggling to survive despite the harsh weather and conditions.
Eventually, the fleeing Northern branches of Xiongnu became the ancestors of the Huns, which would cause indirect destruction and dissolution of the Western Roman Empire in the following centuries.
