There had been a great deal of speculation about the reasons that medieval Europe suffered a dark age while the Islamic world continued and increased its prosperity. The answer perhaps can be found on the contours of the map of the Roman Empire. Islam established its foothold largely in the lands that were fully Roman before the Conquest and ruled from Byzantium after the West’s fall without barbarian interruptions — Syria, Egypt, Mesopotamia, and parts of Asia Minor, in addition to the very civilized Persian Empire — while Latin Christendom gathered strength and established its center of gravity primarily in the wilds of Germania, Western Empire’s lands being devastated by continual barbarian invasions.
Despite the late attempts at politically correct revisionism, it is clear that around the time of the collapse of the Western Empire Europe did suffer demographic, economic and cultural collapse. Gaul and Italy — the most Romanized Latin areas — held out longest against the darkness but, cut off from the lifeblood of civilization, they too could hardly hold out for very long. Another difference is that the Arabs have initially instituted their rule of a thin veneer of a ruling elite over the highly civilized natives, while in the Latin West, religious and cultural homogeneity was valued a great deal higher and the natives a great deal more primitive.