Henri Pirenne – Mohammed and Charlemagne
The Pirenne thesis is that barbarian invasions didn’t collapse the Roman Empire in 476 AD—economic isolation did, two centuries later.
Most barbarians wanted to assimilate, not destroy. They eventually became soldiers, senators, and even emperors who gave their lives fighting for the Empire, sometimes against their own former countrymen. Government and everyday life stayed pretty much the same after Romulus Augustus’ 476 overthrow.
The real change happened about two centuries later, when Arabs conquered most of the southern, eastern, and western Mediterranean. The new conquerors were uninterested in trading with the Romans, and mostly ignored them. This isolated the old Empire from existing long-distance trade.
Isolation from trade caused Europe’s economic decline, as the archaeological record shows (later historians have since confirmed this in detail). Papyrus was replaced by costlier parchment, and churches were lit by ineffective wax candles instead of oil-burning lamps. What once was open became isolated, and that’s what caused the Dark Ages.
Highly recommended, and relevant to today’s trade and immigration policy debates.