Han–Xiongnu War
In 119 BC, when the Xiongnu suffered a catastrophic defeat by the Han armies, the Chanyu moved his court (located in present-day Inner Mongolia) to another location north. This had the desired result that the Xiongnu were separated the Wuhuan people, which also prevented the Xiongnu from exacting many resources from the Wuhuan. The Han court placed the Wuhuan in tributary protection and resettled them in five northeastern commandaries, namely Shanggu, Yuyang, Youbeiping (present-day Hebei), Liaoxi, and Liaodong (present-day Liaoning). A new office, the Colonel-Protector of the Wuhuan, was established (near present-day Beijing) in order to prevent contact between the Wuhuan with the Xiongnu and to use them to monitor the Xiongnu activities. Nevertheless, the effective Han control over the Wuhuan was lacking through much of the Western Han period, since the Xiongnu had considerable military and political influence over the Wuhuan while relations between the Wuhuan and Han often remained strained at best. This can be exemplified by a situation in 78 BC, when the Xiongnu led a punitive campaign against the Wuhuan, resulting in General Fan Mingyou (范明友) leading a Han army to impede further incursions. When they learned that the Xiongnu had left by the time the army arrived, the Han court ordered Fan to attack the Wuhuan instead, killing 6000 Wuhuan men and three chieftains, since the Wuhuan had recently raided Han territory. Only in 49 AD, when 922 Wuhuan chieftains submitted during Emperor Guangwu's reign, did many of the Wuhuan tribes come under tributary system of the Han empire. The Han court provided for the Wuhuan and in return the Wuhuan tribes guarded the Han frontier against the Xiongnu and other nomadic peoples.
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".