Few historical figures are as inextricably linked as Ulysses S. Grant and Robert E. Lee. But less than two decades before they faced each other as enemies at Appomattox, they had been brothers -- both West Point graduates, both wearing blue, and both fighting in the same cadre in the Mexican War. They were not alone: Sherman, Davis, Jackson nearly all of the Civil War's greatest soldiers had been forged in the heat of Vera Cruz and Monterrey. The...