APPOMATTOX, VA. — On April 9, 1865, Gen. Robert E. Lee strode onto the porch of a two-story brick home and stared out at a lawn filled with Union soldiers, his Confederate staff of two, and his horse Traveler. Still wearing full military dress, Lee raised his gloved hands and punched his left fist into his right palm. The sound of leather meeting leather echoed in the unsteady silence. Then, as Lee mounted Traveler, Major Gen. Ulysses S. Grant emerged from the house onto the porch. Now facing each other, Grant raised his hat, as did Lee. It wasn’t a...