Military history of the Three Kingdoms
By the time of the Three Kingdoms period the Xiongnu had already ceased to be a major power. Their last stand as a steppe empire was in 89 when Dou Xian led an army of 45,000 and decisively defeated them at the Battle of the Altai Mountains. The Xiongnu Empire was replaced by a loose confederation of disorganized Xianbei tribes, who were nonetheless highly aggressive and proved problematic to their southern neighbors. A southern branch of the Xiongnu split off from their northern neighbors in 50 AD and continued to exist as a Han puppet state in Bing Province. However, in 188 the Xiuchuge clan rebelled against their Chanyu, Qiangqu, for sending troops to aid the Han against the rebels Zhang Ju and Zhang Chun. They replaced Qiangqu with his son Yufuluo, who's hold on power was tenuous, and he was ousted over a marquis of the Xubu clan. When the marquis of Xubu died the next year an elderly king became the nominal head of state without the title of Chanyu and the Southern Xiongnu ceased to exist as a coherent entity. In 216 the Xiongnu of the Ordos were settled but the region remained outside the jurisdiction of Cao Wei's administration.
Turkic migration
Qin's campaign against the Xiongnu of 215 BCE kept the Xiongnu at bay, driving them out of and seizing the Ordos region. Problems re-emerged after the Qin Dynasty. The Xiong-nu attacked Shanxi of the Han in 201 BCE. Emperor Gaozu of Han bought them off with jade, silk and a Chinese wife for the Shanyu, or leader. Relations with the Xiongnu continued to be troubled and in 133 BC Emperor Wu of Han proceeded against them with 300,000 men. Eighty-one years and fourteen expeditions later in 52 BC the southern Xiongnu surrendered and the northern desisted from raiding. The Han Dynasty military expeditions continued near the frontier of China, in the Han–Xiongnu War, and in 89 AD the Xiongnu state was defeated and soon ended.