Christianity.
At the beginning of the 20th century, there were less than 10 million Christians in Africa. By the end of the 20th century, the African continent had about 380 million Christians. Much of this growth occurred in the last two decades of the century (1980s and 1990s), as missionary activity by native Africans began to expand, and because of high birth rates among African families. So, the beginnings of missionary activity earlier in the century by European and American Christian groups served as a beginning and catalyst for energetic Christian growth by the efforts of Africans who had become adherents of Christianity.
Christianity is continuing its growth in Africa in the 21st century. In its "Status of Global Christianity" report, Gordon-Conwell Theological Seminary estimates that by 2025, Africa will have 688 million Christians and become the continent with the highest total population of Christians.