What accounted for the downfall of Songhay?
a. Defeat and incorporation within the Mali Empire
b. Invasion by the Portuguese in their search for slaves
c. The rise of the Swahili coast power states such as Kilwa and others
d. The collapse of the irrigation system on which the agricultural economy depended
e. Invasion by a Moroccan Muslim army equipped with firearms, followed by internal revolts
Answer: E