I always thought that Christianity is like slavery, you got someone telling you what to do with your life, when to do it & how to do it.
Well… actually, one of the things Christians believe is that God gives everybody the choice to do whatever they want to do. That whole freewill thing. You have available the choice to reject it or accept it, as you see fit. Granted, that doesn’t mean that one choice is as good as the other. Making the wrong choice will have consequences, just like with anything else. But if you do make the choice to believe it, then it makes sense that you need to believe all of it. Believing all of it then requires that you follow the precepts it presents.
But on to why descendents of slaves don’t reject the religion of thier oppressors. Contrary to what some would have you believe, human slavery was not the unique invention of the white man. Slavery has been practiced in almost every culture in the world almost since the dawn of history. According to many of the histories I’ve read, it was common practice throughout history for a people to enslave the people they vanquished. Raids on rival tribes to abduct slaves is an ancient practice. It should be obvious that with slavery being practiced nearly everywhere in the world, many different religions were represented. Especially in places where the religions varied even from tribe to tribe in the same area. Africans were enslaving each other long before Europeans showed up there, and Europeans were enslaving each other too. I would assume that this was a well known fact to all the people involved.
There were simple, practical reasons, too. If your tribe whups up on a neighboring tribe and takes over that tribe’s territory, you obviously will need someone to work the land. For example, if through military victory you’ve just doubled the size of your territory, you probably don’t have enough manpower within your own tribe to now work twice the land (or whatever the needed work was.) So you co-opt the existing labor force and make them do it for you. This was a simple fact of life in primitive society that carried forward into more recent history.
With that scenario in mind, it should be clear that in the majority of cases religion is not a factor in deciding to enslave your neighbor.
As far as the Judeo-Christian realm goes, there are many examples in the Old Testament of Israel drifting away from their own religion in favor of the gods of their neighbors. This happened when they got lax in keeping the practicioners of these other religions out of their borders. So one reason why the slaver would ban the native religion of the slaves would be to prevent the slaves’ religion from corrupting the followers of the slaver’s religion, not simply to take away the slave’s religion.
Add in the fact that both Judaism and Christianity were born out of slavery. The entire original nation of Israel was formed out of Hebrews enslaved in Egypt. Christianity originated while Israel was, for all intents and purposes, enslaved by Rome.
Another thought: if I recall correctly, African slaves in America were intentionally kept illiterate. In fact, it was illegal to teach a slave to read. The primary reason was that literacy would provide a reliable tool for organizing revolts and escapes. Some still learned though, on their own or with help from masters who chose to ignore the law. What single book would be commonly available (one way or another) to the African slaves, no matter where in America they were? I think it’s safe to say that, while the slave owners’ taste in reading material likely varied greatly from one household to another, there was probably a Bible or two in every single household. So slaves who learned to read probably read the Bible along with anything else they had access to. The Bible became the one book that was common to almost all slaves who could read. Because they had the Bible in common, they were able to discuss it amongst themselves, and tell each other about it, and teach it to their children. It became something they could count on being there when/if they were sold to a different owner. It was something that unified them, and provided a rallying point.
Except in this case, the consequences are something not at all obvious, written down a couple thousand years ago by a small Jewish splinter cult that happened to catch on throughout the Roman Empire, and are set up by this same God in such a way that the “choice” is really no choice at all. (“I didn’t throw you into Hell, you chose to ignore the words written down by My Jewish splinter cult. Of course, I created Hell in the first place, and I also created Satan, whom I allowed free reign throughout the Earth to deceive as many people as possible, thereby ensuring that Hell would be well-stocked with Satan’s dupes. But it was your choice, really it was!”)