Coffee has been the fulcrum of life here for almost three centuries, since enslaved people cut the first French coffee plantations into the mountainsides. Back then, this was not Haiti, but Saint-Domingue — the biggest supplier of coffee and sugar consumed in Parisian kitchens and Hamburg coffee houses. The colony made many French families fabulously rich. It was also, many historians say, the world’s most brutal. Ms. Present’s ancestors put an end to that, taking part in the modern world’s first successful slave revolution in 1791 and establishing an independent nation in 1804 — decades before Britain outlawed slavery or...