The Bible documented the existence of a form of slavery in the bronze age Middle East. This was used by God Fearing men of faith who made their livings buying selling and working slaves to justify the thing their very lives and livelihoods depended on. The Bible mentioned it, therefore the Bible condoned it.
As to why the slaves were black Africans, rather than the more traditional Slavic peoples, after all that's where the very word slave (and me!) came from, why any devout Christian could answer that, black skin is the mark of Cain!
I give BenLurkin major major props for recognizing that his opinion is an opinion and that his expertise is not universal. Were that we all were so wise.
Mostly we all, each and every one of us, has a pretty much unlimited ability to justify doing whatever the heck we've set our hearts on doing, for God and Country, for the Children, because (my whackadoodle interpretation says) it's in a Holy Book, or whatever!
I agree 100% that the Bible was used to condone and justify slavery. Even in the New Testament, it was unfortunately accepted as a fact of life, like blue sky, and wasn’t given a moral aspect. In the Old Testament, those passages that can be construed as condemnatory or critical of slavery are not critical of the institution as such, but of God’s people being enslaved. IOW, it wasn’t opposed to slavery, it was opposed to slavery of Jews.
However, the Bible has not a trace of racism in in anywhere, not particularly surprising since the whole concept of inferior and superior races, and indeed that “races” are important, is only a few centuries old.
Those who used the curse of Cain to say black people are intended to be slaves were/are idiots. All of Cain’s descendants died in the Flood, leaving none to populate Africa and provide a convenient source of God-approved slaves.