Trade in Kilwa transformed the local African community culturally.

Evidence

All this trade made Kilwa very rich, but it changed it in more than material ways. … In due course, thanks to these Arab traders, the coastal towns were converted to Islam, and Arabic and Persian words were absorbed into the local Bantu language to create a new lingua franca – Swahili. — Neil MacGregor, A History of the World in 100 Objects, 953

Categorization

• corroborated: 2 independent passages support this claim — Neil MacGregor, A History of the World in 100 Objects, 953