If you look at many history books and ask the question what caused the Dark Ages, you get the following reasons typically: the fall of the roman empire, the little ice age, famine, the black plague and the lack of good roads. These are found for example here!

The problem with these supposed "causes" is they are mostly effects, not the underlying causes. They don't explain why Europe's economy went off a cliff edge and didn't recover for a millennium. Nowhere is the war the Byzantines had with the Persians considered as a factor. Nor is the advent of the Islamic empire considered. In my latest book, A Pedal Pilgrimage in the Nordics, I propose another theory, one that is backed with solid evidence. It is quite surprising that historians till of late have not referred to this reason which is very strange indeed. Please feel free to share your thoughts on this question below.