Justinian's Flea

I recently read William Rosen's Justinian's Flea, an account of the plague that devastated the Byzantine Empire around 540-542 CE.
Rosen mainly argues that in the west, the reduced populations in northern Europe forced a revolution in farming techniques. More advanced techniques were necessary after the reduction of the availability of cheap labor and secured the survival of the Germanic tribes in Europe. Consequently a feudal society emerged from the plague and defined the developments throughout the middle ages until the second visit of Y. Pestis in 1347-48, which again changed the cultural, economic and political landscape of Europe.
My interpretation is that Justinian’s plague allowed the Germanic tribes to settle permanently in various locations in western Europe, including Italy, and to establish new societies based on Christianity and a feudal economic hierarchy. Indeed, it is only after Justinian’s plague that the tribal movements stopped and these tribes settled in the areas that they had conquered up till that time. It is in these areas that they established their feudal societies and built their Gothic churches.