Blackness invites speculation. The very idea of a global African diaspora creates the most fertile of grounds for a field of what-ifs. What if European enslavers and colonizers had never ventured into the African continent? More intriguing yet: What if African nations and peoples had successfully rebuffed generations of plunder and theft? What if the Zulu had won the wars against the Voortrekkers and the British, and a confederation of Bantu people had risen up and smashed Belgian rule? What if the Transatlantic children of the mother continent had been allowed to remain, building their empires with the bounties of...