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.
Origin of the Huns
At the beginning of the twentiethcentury, German Sinologist Friedrich Hirth discovered passages in the Chinese annals that he believed proved the connection between the Huns and the Xiongnu. Hirth's work convinced many, and by the 1940s there was a general consensus among historians and archaeologists that the Xiongnu and the Huns were related. However, Otto J. Maenchen-Helfen showed conclusively that Hirth had misinterpreted the Chinese annals in 1945. Maenchen-Helfen also argued against the identification based on then-current archaeology and on ethnographic grounds. While he did not address the question in his most important work, "The World of the Huns" (1973), Maenchen-Helfen would go on to cast doubt on new theories that equated the Huns and the Xiongnu on the basis of their names in several articles. Maenchen-Helfen's skepticism was also taken up by prominent Eurasianist Denis Sinor.