Okay. But this does not answer the question whether black slaves were freed from slavery once they adopted Christianity as a religion !
First, this not the reason why slavery ended in America. Second, Types of slavery like "penal servitude" persisted in America up well into the 20th century. Third, many if not most slaves in America were generations of Christians while they were slaves.
The quran and hadiths had praised manumission as a meritiorious act. Many slaves were freed in this regard and Muhammad himself set an example by freeing and marrying a woman named Safiyyah bint Huyayy in this manner, and freed and adopted as his son Zayd ibn Harithah.
Slavery was a preexisting Arabian practice and Islam considerably reduced the barbarity of this practice even if it did not completely eradicate it.
This describes some of the aspects of slavery in Islam, and does not address the fact that slave trading and slavery was very much a part of Islam throughout its history.
The theme of the thread deals with how religion has acted to abolish this primitive and unethical economic and social trend.
Christianity nor Islam had scripture forbidding slavery. The Baha'i Faith is among the first to unconditional forbid all forms of slavery