How did the southern economy differ from the northern economy?

I think the northerns earned money by selling cash crops and southerns sold products they made.

Explanation:

 I really hope this helps! Sorry if I am wrong.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).