Final answer:
Arabic spread through Africa because of the trans-Saharan trade due to the diffusion of Islam by Muslim Berbers. The spread and adoption of Islam helped expand networks of exchange and increased trade.
Step-by-step explanation:
The language Arabic spread through Africa because of the trans-Saharan trade. The ideas of Islam were diffused by Muslim Berbers along the trade routes they used, penetrating West African trading towns. The spread and adoption of Islam by nomads and traders helped expand the networks of exchange, and the shared language and values among devout Muslim traders facilitated trust and increased trade.