What would it take to keep north Africa (Tunis/Carthage areas in particular) as insanely wealthy as it was during the Roman and early Arab eras? Would avoiding the 7 years siege of Tunis (and killing 100,000 people) help north Africa stay wealthy? Is it possible to have an empire that spans the coast of north Africa?
Try to come up with scenarios for all this. Start at the 11th century.