September 30, 1919. The United States teetered on the edge of a racial civil war. Racial fighting had erupted in 25 cities. Deep in the Arkansas Delta, black sharecroppers formed a union to sue their white landowners, who had cheated them for years. What happened next has long been shrouded in controversy. Over several days, posses and federal troops gunned down more than 100 men, women, and children. White authorities arrested more than 300 black...