Sometime from 1900 to the present day, create a situation in which the African American population has its own "homeland", this can range anywhere from something to similar to the reservations of the Native Americans or as far as an actual independent nation within the borders of OTL USA (or in the Caribbean, or even Africa, although both of these require of mass migration).
(Please no flame war on this, and also as a rule I'd like to add that discussing future events to create such a state is not allowed, we are talking purely historically).