Germans
The Germanic peoples during the Migrations Period came into contact with other peoples; in the case of the populations settling in the territory of modern Germany, they encountered Celts to the south, and Balts and Slavs towards the east. The Limes Germanicus was breached in AD 260. Migrating Germanic tribes commingled with the local Gallo-Roman populations in what is now Swabia and Bavaria. The arrival of the Huns in Europe resulted in Hun conquest of large parts of Eastern Europe, the Huns initially were allies of the Roman Empire who fought against Germanic tribes, but later the Huns cooperated with the Germanic tribe of the Ostrogoths, and large numbers of Germans lived within the lands of the Hunnic Empire of Attila. Attila had both Hunnic and Germanic families and prominent Germanic chiefs amongst his close entourage in Europe. The Huns living in Germanic territories in Eastern Europe adopted an East Germanic language as their lingua franca. A major part of Attila's army were Germans, during the Huns' campaign against the Roman Empire. After Attila's unexpected death the Hunnic Empire collapsed with the Huns disappearing as a people in Europe – who either escaped into Asia, or otherwise blended in amongst Europeans.

Q: Which Germanic tribe did the Huns cooperate with?
Ostrogoths