"The slaves were sold into slavery by black, African chieftains. Many American blacks probably wouldn't be alive today if their ancestors hadn't been sold (due to disease and war in their native countries)."
This remind me of something I read several years back. It by no means condones the tragedy of slavery, but it fits with what you are saying.
It might have been the late eighties or the early nineties. Mohammed Ali was on a trip to Africa. What he saw there was grim enough to prompt him to remark, "Thank goodness my relatives got on that boat." I remember thinking at the time that, from the aspect of one who was a descendant of slaves, he had made a truly honest comment.
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The book Out of America: A Black Man Confronts Africa by Keith B. Richburg deals with this.