In November 1864, Gen. William Tecumseh Sherman left Atlanta, Georgia in flames and embarked on his historic Great March from Atlanta to the Sea. Along the way, he unintentionally liberated thousands of Black people held as slaves in the Georgia cities and towns. Some joined the Union lines as hired servants, cooks, laundresses, teamsters, and pioneers. Others joined "for their actual freedom." In numbers reaching tens of thousands, they became Sherman's Fifth Corps, and one of them, a young ex-slave named Jennie Lewis, became Sherman's mistress. Through actual and fictional letters, diaries,...