There has been several "great migrations" in history: 1,500ish years ago Europe was totally transformed as tribes like the Goths, Vandals, Angles, Saxons, Lombards, Suebi, Frisii, Jutes and Franks were pushed westwards by e.g. the Huns, Avars, Slavs, Bulgars and Alans. In all a very few million...