Your second paragraph reminds me of Pat Buchanan’s thoughts on what the slaves received from the deal. The greatest of which, is Christian Salvation through The Lord Jesus Christ. There will be multitudes of blacks in Heaven who would otherwise have been eternally lost. That does NOT excuse slavery, but it does show how God can bring good even out of something intrinsically evil.
Even as he gave Obama a second term to make sure we were ready to elect Trump this time around. He (God) is awesome!