Top 3,
In fact the islamic faith also has deep roots in east africa and it is misleading to say it is largely confined to north of the sahara. In Eritrea the split between islam and christian faiths is almost exactly 50/50 and ethiopia is the same. For all their problems one of the triumphs in these two countries is that the religious divide has not torn them apart.
It is even more remarkable because the two faiths are distributed around the country rather than being confined to discreet geographical areas. Djibouti and Somalia are predominantly muslim; remember Ahmed Salah ? Meanwhile in Kenya and Tanzania the coastal areas are heavily populated by muslims. Evidence of the islamic influence runs deep. Some of the architecture is stunning. This can be traced back to the travels of middle eastern merchants using the monsoon winds to take their boats back and forth between arabia, east africa and india a thousand years ago, long before the christian missionaries arrived.
And remember the effect of the arab slave merchants who progressively went inland to find people and at the same time spread their islamic faith.
Even in inland areas there ares sizable muslim populations and you will find mosques dotted everywhere. While it is accurate to say that most of the runners from Kenya have christian faiths there are exceptions e.g. Ibrahim Hussein. The same is true in Ethiopia, Mohammed Kedir (who i think won silver behind yifter ??) was not christian.
Salam Aleykum