[Cronos]

Good example of Byzantium. I would argue that the Byzantines just had bad luck -- in the 7th century they were exhausted from defeating the Sassanids and then they faced a 2 pronged war: Bulgars and Arabs

and, they pushed back the Arabs in the 9th century but then a new, virulent Islamic power, the Turks came to fore

in fact that seems to be the case even in Hispania: first the Arabs, then the Almohad, then the Almoravids, each wave coming, initially virulent and then weakening and replaced by another virulent strain

The only way the Spanish got rid of them permanently was a virulent expulsion

that's where I give you my hypothesis of a civilisational virus that is Islam -- infecting a host and initially very virulent, but then dormant until a newer strain comes

[Sherman Logan]

All true, except you switched the Almohads and Almoravids in time.