The correct answer is - Christianity.
The African slaves that were brought into the New World brought multiple different religions with them, but they were pagan religions, and that was not seen very fondly by their Christian overlords, nor by the Christian missionaries.
Once the slaves were brought into the New World a process of conversion was started. While some of them accepted the Christianity willingly, others did not, so they were punished, tortured, and forced to practice it. The end result has been that all of the slaves ended up following the Christianity as their religion, and most of them are still practicing it nowadays.
