I'm not going to write an essay here; I just want to point you in some directions to contemplate and research if this is an area of interest to you. This is another case study for my "faith and reason" and "discernment" series on how to improve clarity of thought and the taking of personal policy positions, especially for young readers who did not live through the times and do not have a lot of the context and information.
1) Slaves brought to the USA came from different tribes with different cultures, languages and faiths. Therefore you must realize that there was not one pan-Africa uniform native faith from which slaves were uprooted. There were many and remember that ancestral faiths tend to be tied very much to the actual homeland, and thus is near impossible to hold onto. For example, think of the many tribal faiths around the world, including for example the Navajo Native Americans here in the USA, who link their faith to landforms such as sacred mountains. So a transplanted slave from Africa had little chance to continue their faith when removed from tribe, kin and the land. Another example is that even today it is hard for public health officials to spray ponds near African villages with insecticides because even if dangerous diseases are rampant in a pond, the pond itself may be viewed as sacred and essential to the traditional faith. So how would a captive from a tribe and a village with a sacred pond maintain their "faith" when transplanted across the ocean to America, or anywhere else? Faith was extremely local, often on the village or tribal level; it was not a uniform experience throughout black Africa.
2) Slaves were very spiritual and strong in belief, so they adopted in many cases willingly the faith of the slave owners and the community. This meant Protestant faiths. Catholics were a non existent culture so far as being slave owners, and had only one major outpost which was New Orleans (where there was French settlers). So this is why the vast majority of today's Afro-Americans have Christian faith that is post Reformation based and not Catholic. (You can see the reverse among Native Americans who were under Spanish influence, who had Catholicism imposed upon them in their native lands. Some were evangelized and willingly converted, but remember, they were still in their ancestral homes among their tribes, kin and land and thus were not loosened from their faith base as Afro-American slaves were when taken out of Africa homelands).
3) Afro-Americans are by nature and tradition very spiritual and faith based, and so they evolved the black church tradition that is a monument of faith. What I am saying is that they did not accept "the bare minimum" of faith necessary to survive, but took Christianity to their own and embellished and amplified it in a remarkable way that is a testimony to God's presence in their life. It is not just a matter of the outward signs, such as gospel choirs and enthusiasm for revivals, but these embellishments to the faith, plus the planting of many small local churches were signs of their deep inner faith.
4) Today in Africa itself there is a huge voluntary conversion toward Christianity, both the Protestant form and the Catholic faith.
5) During the Civil Rights movement the Christian faith held by Afro-Americans was instrumental in their determination, non violence, and cohesion of family even in the face of poverty and resistance.
6) During the "black liberation" movement that is an offspring of the Civil Rights movement, it became a legitimate question but veered into revolutionary faddism, to question whether "descendants of slaves should hold the religion of their 'slave masters.'" This is why a strong movement toward Islam (though a "black" version of it in many cases) emerged. The good part of it is the determination to believe in one God, the God of Abraham. The bad part of it is the notion of tinkering with creating yet another model for denominations and faith systems based on politics, social reactionaries, and assuming that what has been forced on someone must by definition be wrong in its core.
Those who did not go with the Muslim option often did one of two alternatives. They developed radicalized "black churches" that use Jesus Christ to promote their social agenda and veer away from devout worship of God as is or they were tempted to try to create an imaginary "recapturing" of the "faith they left behind in Africa." So you get things like Kwanzaa but if you really examine them you could never match them to the beliefs of the actual slaves who were first brought to the USA (remember I pointed out that faith system was tribe, kin and location based). So you get an amalgamation that is political and not actually pure to the genuine African faith history. That's fine if that's what you want but don't market it as being what ancestral slaves would have actually worshipped!
7) As Afro-Americans became if not middle class and wealthy but at least with incomes from jobs or from social services, they started being viewed by the economic upper classes less as a labor force and more as "consumers." As a result the Christian faith of Afro-Americans has been both intentionally and inadvertently targeted for weakening by those who have product to sell that is contrary to the faith of traditional older Afro-Americans. That is an entirely unique situation and I'll let you think that through. Do because it's very important. (Hint: you don't see products being marketing just to Catholics or to Native Americans that are contrary to their faith, though they are examples of groups that get caught up in the general consumerism. No, Afro-Americans have faith busting products marketed specifically to them for purely consumerism reasons... like rap, prison chic and sexualizing "ho" products). Another hint: Planned Parenthood marketing abortions to black neighborhoods, a long time scandal that I do not understand why people are not informed and totally repulsed.
8) New age has crept into the faith weakening game in a number of ways. The most classic example is the "lost tribe" angle. This is always a temptation for any group around the world, to legitimize themselves and boost self esteem by trying to create a prominent place for themselves in traditional faith history (like being "the lost tribe" from the Bible) or to imagine a glorified reason for suffering and oppression (that's the hook that new agers use to push "past lives," "aliens," etc.) There is also a phony "Eve chic" that is marketed to Afro Americans. The "logic" is that Eve "must have been black" if she was the "first woman" and therefore her disobedience is subject to revisionist thinking that "hmm, well, already she was oppressed by God and the prevailing proto-Jewish society, so wow, hmm, maybe she really is a big fertile sexy goddess who 'got framed' (to quote a bumper sticker I saw in Albuquerque). Let me assure you, Eve's disobedience to God was total and spans all colors.
It is a credit to the strong Christian black churches how they have not sought glorification that they do not need through these temptations to make up fake faith history and insert themselves in it. Real Christians recognize that all are equal before God and that they do not need phony mystic, self glorification and so forth. Afro Americans who fall for the new age garbage ($cientology is another example) exhibit their own insecurity and lack of understanding that faith in one God who loves all equally raises them to the banquet table; they don't have to make up anti-God spirituality and step on other people's faces in order to become "higher."
I hope these fact based points give readers who are interested in this subject a good area to do further study and reading (real history please!) If nothing else, remembering the points I've made will help you to understand some of the changes, churning, misunderstanding and conflict that is going on today, and also is informational about the problem of violence (Birmingham, Alabama is a case study) and the disintegration of the family.
Homework assignment! Here is an example of taking a point I've listed and doing more FACT BASED reading. In point 1 I mention sacred ponds, read about the Sacred Pond of Ogi in Nigeria. http://www.nytimes.com/2006/03/26/international/africa/26worm.html