The author states that "Christianity and Islam share a fifteen-hundred-year history in Africa" – briefly describe what this history is (main points here – please don't recopy whole sections)

Yes, they share the history.

Explanation:

Fifteen-hundred-year ago Christianity is the main religion of African people and with the invasion of Muslims on Africa and conquering many areas, many local people impress from Muslim's behavior and accepted Islam. Christianity was the religion of american people from a long time while it was the initial days of Islam so we can say that Christianity and Islam share a fifteen-hundred-year history in Africa.