His friends called him “Sam.” His wife called him “Lyss” or “Victor.” His initials inspired a nickname tied to one of his greatest battlefield triumphs: “Unconditional Surrender Grant.” He quietly told his brother in April of 1861, while walking home after a recruiting meeting in Galena, Illinois, “I am in to do all I can.” And so he did. The unassuming Grant never expected to play a significant role in the Civil War, yet by its end, commanded every soldier in the United States armed force...