III. MONGOLS, 1st Wave:
Hsien-pi: They originated around what is now the border between Mongolia and Manchuria. They were a loose, unorganized grouping of tribes. In alliance with the Chinese and the Southern Hsiung-nu, they conquered the Northern Hsiung-nu in 87-89 AD. Before the final defeat of the Northern Hsiung-nu, the Hsien-pi liked to deliver severed Northern Hsiung-nu heads to the Chinese in return for bounty money. But after the Northern Hsiung-nu were finally defeated, this source of cash dried up. The Hsien-pi reacted by turning on the Chinese and launching raids against them. Starting in 156 AD, a Hsien-pi chieftain named T'an-shih-huai put together a consolidated Hsien-pi empire that successfully made war on China. However, his empire collapsed with his death in 180 AD. (Note that the Hsien-pi did not take the head of the chieftain of the Northern Hsiung-nu. Instead, they peeled off his skin and kept it as a trophy.)
Ju-juan (or Juan-juan or Rouran): They called themselves "Ju-juan." But the Chinese made a pun on their name and turned it into "Juan-juan," which means "nasty wriggling insects." They ruled what is now Mongolia. A chieftain named She-lun unified them into an empire around 394 AD. They were allies of the White Huns. The Ju-juan fought against the Turkic Toba constantly when the Toba ruled northern China. They were defeated and chased west by an alliance of the Gök Turks and the Western Wei of the Toba in 552 AD. They joined with the White Huns to form the Avars in or shortly after the 560s AD.
Avars: The Ju-juan, and the White Huns, both on the run from the Gök Turks, united to form the Avars in or shortly after the 560s AD. (Some experts assert that a group called the "Chionites" morphed into the Avars after being defeated by the Gök Turks around 558 AD.) Subsidized by the Greek Christian Byzantine Emperor Justinian's gold, the Avars swept west through the Ukraine in the 6th Century AD, overrunning the Alans and the Sabirian, Utiger, and Kutriger Huns along the way. When Justinian's successor, Justin II, suspended payments to the Avars, they turned on the Byzantines, raiding Byzantine provinces along the Danube River. Led by their warrior chieftain named Bayan, the Avars established their base on the steppe-like plains of what is now Hungary in 565-568 AD, destroying the Germanic Gepid tribe as they did so. Bayan led his warriors on raids into central Germany in 562 and 566-567 AD, leading to skirmishes with the Germanic tribe of the Franks (who eventually became the French). Once in Hungary, the Avars alternately fought for and against the Byzantines according to the effectiveness of Byzantine bribes. The Avars reduced the indigenous Slavic peoples to servitude and drove large numbers of them to migrate into the Balkan provinces of the Byzantine Empire.
The Avars were notable for wearing heavy armor in battle and for being probably the first people in Europe to use iron stirrups for riding horses. Their leaders also had armor for their horses.
The Avars continued to terrorize central and southern Europe for some time. They raided into Austria and Italy. Their power was diminished by a revolt of their Slavic underlings in 623 AD. In 626 AD, in conjunction with the Sassanid Persians, and led by Bayan's son and successor, they attacked the Byzantine capital city of Constantinople but were decisively repulsed. Charlemagne (the Frankish king who was the first emperor of the so-called "Holy Roman Empire") conquered the Avars in 791-799 AD. Charlemagne's conquest was helped by Avar disunity and civil war. One of several competing Avar chieftains, a man who had just been Christianized, gave part of his lands to Charlemagne. An Avar revolt in 802 AD was suppressed by Charlemagne. The surviving Avars became Christian and gradually disappeared as a distinct people.