Confined to her bed in Atlanta by a broken ankle and arthritis, she was given a stack of blank paper by her husband, who said, "Write a book." Did she ever. The novel's first title became its last words, "Tomorrow is another day," and at first she named the protagonist Pansy. But Pansy became Scarlett, and the title of the book published 70 years ago this week became "Gone With the Wind." You might think that John Steinbeck, not Margaret Mitchell, was the emblematic novelist of the 1930s, and that the publishing event in American fiction in that difficult decade...