I was looking at a map of the Roman empire and noticed that there were many cities clustered in Western North Africa. There were also some real heavy hitters like Carthage, which obviously was destroyed. There were also a lot of prominent North African thinkers in the Roman Empire, the first which comes to mind being St. Augustine. We rarely ever hear about North Africa post Rome. I know there was the Arab Conquest, and the Moors were pushed out of Spain back into North Africa, but why did it lose its prominence in the affairs of the region?
Not going to pretend that I’m an expert in this area but I’ll give it a shot.
Roman North Africa was the granary of the empire; providing cereals, olive oil etc. as well as the production of Red Slip pottery, used by almost everyone and found throughout the empire. NA was essential for the supply of food to Rome as Egypt was to Constantinople.
The Vandal conquest of the region put an end to that. Gaiseric used the reliance of Rome on NA foodstuffs to essentially blackmail the capital as and when he chose. The trading fleet was turned into a large pirate fleet, further disrupting trade. The Vandals themselves were not much in the way of sailors and used Roman Africans whom they began to persecute due to not following Arianism, damaging the economic arm of the state.
The Vandals seem to have retained a Germanic style of rural, land holding aristocracy. They didn’t fill any of the city-based niches of the Romans, considering how few Vandals there were in comparison a decline in cities probably would have helped consolidate their power as an urban population is more difficult to control with a small occupying force. You stop seeing red slip pottery in other parts of Europe by the 7th century suggesting a breakdown of both production and trade.
The Eastern Romans reconquered Carthage in 534 but the strategic importance of the area was finished. Carthage is very convenient for supplying the Western empire but much less so one centered in the East. It becomes an outpost of empire, quite hard to keep track of (it is essentially an independent state by the time of the Muslim conquest). With NA’s absorption into the caliphate you see the same problem of distance creating irrelevance, it makes no sense exporting grain to the rest of the empire when they have to pass Egypt, another food producing region, on the long voyage. The antagonistic relationship with other Mediterranean states also puts a stop on ocean trade.
So in short I think geopolitical reasons created an obstacle to trade leading to a decline. I don’t think the trans-Saharan trade was too developed then, this was to be a source of wealth for later Moroccan rulers. I also remember reading somewhere that climate change occurred around that time limiting food production, but, like I said, I’m not expert in this area.