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
There is a gap of about two hundred years between the conquest of the Xiongnu by the Xianbei and their disappearance from Chinese historical records and the appearance of the Huns in Greco-Roman sources. According to the "Book of the Later Han", the final known Xiongnu emperor either disappeared to the west or moved to the territory of the Wusun in modern Kazakhstan in 91. According to the "Wei shu", they then moved further west to around modern Tashkent, where they were defeated by the Xianbei in 153after this, nothing further is recorded about them for twocenturies.
Denis Sinor argued that the origins of the Huns cannot be established beyond what it is said in the work of Roman historian Ammianus Marcellinus: Ammianus said that the Huns dwelled beyond the Sea of Azov next to "the frozen ocean" before they entered Europe, though Sinor does not take "frozen ocean" literally. Both he and Maenchen-Helfen, meanwhile, note that Ammianus refers to the Huns having been "little known", not unknown, before they appeared in 370: they connect this with a mention of a people called the "Khounoi" by the geographer Ptolemy in the mid-second century. Maenchen-Helfen notes, moreover, that the fact that the Huns were not noticed before 370 is not proof that they came from far away, comparing them to the ancient Hungarians: "We know by now that the Magyars (Hungarians) lived for three hundred years practically unnoticed by the Byzantines in the region of the Dnieper, Bug, Dniester, Pruth, and Sereth before they swept over Central Europe very much like the Huns".