All the Huns did was start in China and move West taking local brides along the way ~ an old Hun passtime!
Here's an example of what's meant by "slavery". Let's take the Iroquois Indians circa 1300. They were tributary to the Huron. They revolted and fled South from the St. Lawrence into the highlands of Central New York ~ and along the Mohawk.
The Great Lawgiver showed up; directed them in "how to do it right" and they became free people. Shortly thereafter they began a multi-hundred year war with the Mohicans ~
The Germans seem to have been tributary to the Celts all along the Volga. No doubt they occasionally ran off into the woods, but about 300 BC (a good thousand years earlier than the Iroquois) they mounted a general revolt against the Celts who then fled to bases of operation around the Black Sea and the Mediterranean.
The same thing happened several times earlier.
The Germans have grammatical elements in their languages that derive from Fenno-Scandia ~ which clearly denotes their earlier experiences with Uralic-Altaic speakers as well as the Sa'ami. No doubt when the Germans ran off to the woods they ran to the North Woods.