[AlexanderHowl]

If I remember correctly, the Bantu-speaking people did not enter what we call the Swahali Coast until around 500 AD (the area was occupied by Cushitic peoples, Khoisan peoples, Nilo-Saharan peoples, and the Pygmy peoples). The introduction of Roman trade and organization may have allowed to people native to the region to repulse the Bantu migration, preserving the ancient cultures and the ancient peoples that were destroyed by the Bantu-speaking people. It would have been much different than the region in our world.

I disagree about Islam not evolving. If Rome holds Mecca, then Islam spreads through the same trade networks that Christianity did, meaning that it spreads throughout the Romans Empire, just like Christianity did. Or perhaps that change in the timeline prevents the spread of Christianity which, in turn, prevents the emergence of Islam.