In 375 AD, the Huns, a Mongolian people, arrived in the region of present-day Ukraine, destroying the German Ostrogothic kingdom that had been established there. The advance of the Huns sparked mass migrations of German tribes into western Europe. Divided into many clans, the tribal leader Attila made himself high king or "kagan" and united all the Huns after 441 AD. The Hun empire grew rapidly under Attila, including people from many different cultures, and not all were unwilling followers. Following the collapse of Attila's empire after his death in 453 AD, the remnants of the Huns, called the Bulgars, formed a small kingdom on the Volga River.

The first Mongolian empire in central Asia is destroyed by a revolt of some conquered Turkish tribes in 552 AD. The remnants of the Mongols, called the Avars by the Romans, flee westward towards Europe. The Avars united with some Bulgar and Slavic clans and established a kingdom under the Kagan Bajan (565-602 AD), in the region now occupied by Hungary.

The Khazars unite into an empire and end Sarmatian dominance of the Black Sea steppes. The Khazars were a semi-nomadic people who engaged in both farming and trade. Tariffs collected from trade routes through their territory allowed the Khazar kings to raise and pay for a standing army. They defeat the Bulgars around 650 AD, some of whom flee to the Danube area.