After a long period of secure Roman rule, from the 320's Pannonia was again in frequent war with the East Germanic and Sarmatian peoples to the north and east. Both the Vandals and the Goths marched through the province, causing huge destruction.^[6] After the division of the Roman Empire, Pannonia remained under the rule of the Western Roman Empire, although the district of Sirmium was actually more in the sphere of influence of the East. As the Latin population of the province fled from the continuous barbarian incursions,^[7] Hunnic groups began to appear on the verge of the Danube.

In 375 CE, the nomadic Huns began invading Europe from the eastern steppes, instigating the Great Age of Migrations. In 380, the Huns penetrated into present-day Hungary, and remained an important factor in the region well into the 5th century. The Pannonian provinces suffered from the Migration Period from 379 onwards, the settlement of the Goth-Alan-Hun ally caused repeated serious crises and devastations, the contemporaries described it as a state of siege, Pannonia became an invasion corridor both in the north and in the south. The flight and emigration of the Romans began after two hard decades in 401, this also caused a recession in secular and ecclesiastical life. The Hun control gradually expanded over Pannonia from 410, finally the Roman Empire ratified the cession of Pannonia by treaty in 433. The flight and emigration of the Romans from Pannonia continued without interruption until the invasion of the Avars. The Huns, taking advantage of the departure of the Goths, Quadi, et al., created a significant empire in 423 based in Hungary. In 453 they reached the height of their expansion under the well-known conqueror, Attila the Hun. The empire collapsed in 455, when the Huns were defeated by the neighbouring Germanic tribes (such as the Quadi, Gepidi and Sciri).