I didn't know that either, but according to Dr. Elliot Engel, the story is really the masked autobiography of Margaret Mitchell, the book's author.
"'Gone With The Wind' is one of the most popular novels and motion pictures of all time, but you will be surprised when you learn the real story behind the novel and the glamorous Hollywood legends surrounding the film. Few know that the novel has little to do with the Civil War and the Deep South, but is really a glimpse into the real life and loves of Margaret Mitchell," said Engel.
"Mitchell was a shy woman," Engel said, "and 'Gone With The Wind' is her secret autobiography. She wove important events of her life into the storyline." Hmmm.