From pp. 217-218 of Mark Perry's Grant and Twain:
[ Later, in looking back on his life, Twain admitted what he had discovered about himself in India: that the central and singular fact that had shaped his time and shaped him was the question of slavery -- that "bald, grotesque and unwarrantable ursurpation" of human freedom that "stupified humanity." And at the heart of slavery was the question of race, of racism -- which is what made slavery possible. Race was present, for Twain, everywhere he turned: in this Missouri childhood, in his recollections of "Uncle Dan'l," in the face of Tom Lewis at Quarry Farm, in the strange behavior of his next-door neighbor Harriet Beecher Stowe, and in his own writing. It was this, the question of race, that so attracted Twain to Grant. In Grant's struggles Twain saw his own. Like Twain, Grant turned the question of slavery, and race, over and over in his own mind and faced with it each and every day. Raised by an abolitionist, he employed his father-in-law's slaves, remained silent when his wife defended the institution, and assiduously ignored the calls for racial equality when he was president. Grant condemned slavery and fought against it, and he abhorred racism. But he could not overcome it. Like Twain he believed the nation's soul was infected by racism, but not his. Why?
Why was it that after the loss of more than six hundred thousand Americans in a catastrophic civil conflict, men like Twain and Grant could not complete the victory sealed at Appomattox? Why, deep into their own century, could they not stay the hand of southern (and American) injustice, which freed the slaves to be citizens but then denied them their rights? Books, theses, and endless monographs would be written on the subject in the decades following the passing of Twain's generation, but the simplest answer might well have been uttered by Sam Grant as a commander in Tennessee. One day, observing the lines of the thousands of former slaves following the army, he turned to John Rawlins, one of his closest aides. "I don't know these people," he said. ]