Like some people have said they seem tribal too me. They don't have horses, good armor, or even good weapons ... just simple spears and crossbows. Crossbows don't take any skill compared too bows. They're definitely not
just defending themselves, I've noticed they're pretty aggressive so I'm guessing they're supposed too be some kind of primitive tribal faction out for loot and women.
As far as who they resemble in history ... possibly some primitive tribe from the edges the steppes migrating into eastern Germany ... not exactly a steppe tribe with horse archers and all that, but they definitely know how too defend themselves from the cavalry types: an absolute must for a steppe tribe.
Maybe ... just maybe we'll see them get some sort of war wagons or something ... and pavises for the crossbowmen! that would be sweeeeeeet.