Have Chas Goodyear be black and a good businessman. Or have Harvey Firestone be black.
Or have Frederick Douglass get behind the idea, though I think it repelled him. AFAIK one of Douglass' main beliefs was that blacks in America were Americans and had as much right here as anyone else native born
George Washington Carver accepts Edison's offer of a hundred grand salary and then later uses the money to finance his own research lab partnering with Edison into the uses of rubber and other tropical goods in Liberia. This is partially due to his conversion to Marcus Garvey's movement, but when Carver sees Garvey as a mountebank he throws him out in a coup engineered by one Reverend Little, one of Garvey's preachers who in OTL fathered Malcolm X.
American backing to keep the strategic rubber out of Axis hands in WWII results in Liberia becoming the unoffficial US catspaw in Africa. As time goes on their position as the world's black "homeland", based on an American equipped and African manned army second to none in the world, becomes more and more powerful and secure. The American black liberation movement comes much earlier (late 40s') and is much more successful. South Africa and Rhodesia avoid apartheid and follow a Kenyan based model, under Liberian tutelage and control. The Congo and Uganda, unfortunately, fall under socialist dictatorships but even there the main abuses and problems are much mitigated.
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