@TG:
The Hun Empire, only tribute from the Romans prevented them from become conquered slaves like the Germans were.
Somewhat true. There were 75 years, from 375 to 450 AD, were the huns pressed on europe.
But, if you look for Huns, who were nomads, as slaveholders, you probably will rather find them treat their conquered people like Ammianus Marcellinus writes in his ROman History, book 31, chapter 3.
“Igitur Huni pervasis Halanorum regionibus, quos Greuthungis confines Tanaitas consuetudo nominavit, interfectisque multis et spoliatis reliquos sibi concordandi fide pacta iunxerunt eisque adhibitis confidentius Errnenrichi late patentes er uberes pagos repentino impetu perruperunt, bellicosissimi regis et per multa variaque fortiter facta vicinis nationibus formidati.”
They looted and plundered, and then forced treaties onto the beaten people. Slavery is not directly mentioned, maybe because it is part of looting for a Roman.
It’s hard to tell. More important is the when and for how long if you look for effects. But, you are right, there were other cultures oppressing cuacasians. The effect of that (apart from starting the great movement of people and thus the fall of rome etc.), so the direct effect i would think is neglectable, compared to the indirect effect (as the merging of germanic and roman culture, thus setting the way for christianity and the Holy Roman Empire, and all that follows).