@tomservo50: "The history of the Great Migration in Europe included the likes of Goths, Vandals, Angles, Saxons, Lombards, Suebi, Frisii, Jutes, Franks, Huns, Avars, Slavs, Bulgars and Alans"
The goths who are known for sacking parts of Roman lands in there migration, the Vandals who did the same, The Angles conflict with the Saxons who invaded there land, The Lombard's who moved south and conquered parts of Italy, Suebi where a proto-germans who fought the Roman conquest of Germanic and so on and so fourth.
Now hers the thing ohter then the fact that they "migrated" by conquering land and and most of these groups where indo-Europeans who migrated around Europe.
Find me a mass migration after the establishment of the nation states. After the Barbers where driven back by the franks and the creation of the Frankish empire. OH and show me the mass migration of Africans to northern Europe that would facilitate this diversity in a story that uses Poland as a backdrop.