Ok, we have the black death ravage Europe far more severely than in OTL, killing 4/5 of the population. The survivors, despairing of civilisation, flee to relatively unharmed Scandanavia. There they try and re-build as best they can. We have a lot of English, a lot of Germans.
Or, more realistically, Viking slavery. They Vikings take slaves from Britain etc. and set them to work. . .
Or, more realistically, Viking slavery. They Vikings take slaves from Britain etc. and set them to work. . .