This may sound far fetched as in a "final solution" to the black question, but in reality in the early 20th century there were numerous instances where blacks in the US found themselves sterilized against their will, this was within the eugenics boon of that period.
What if this taken to wider-scale mirroring the holocaust of the Jews but instead of actually mass killing an ethnic it was widespread mass sterilization with the intention of eliminating that population group?