On a rainy night in early 1865, Secretary of War Edwin Stanton arrived in Savannah, Ga. — which the Union had captured weeks earlier — with a question: What should become of newly free black people? It was a question that many in power had been asking for some time. What was different this time was to whom the question was posed: the newly free black people themselves. It was a visit born of a massacre about a month before, and it launched a debate that continues to this day. The issue of where these people should go had dogged...