Written in 1953 about what might have happened if the South won the American Civil War, this is a thoughtful novel with a twist in the tail. It is expanded from the original short story, and while some reviewers have argued that the additional material is padding, I feel that it adds to the novel if one reads it more than once.
With hindsight one might say that the alternate time-line depicted is Steam-punk, but Ward Moore anticipated that by half a century. Others might claim the novel is dated, but I feel his style adds to the charm, and sets the environment in deeper, more subtle colours, and reading it again recently I enjoyed it far more than any of the dozen or so modern "SF" books I have read in the last year.
The pace is deliberate and the characterisation is secure, and there are no whizzy spaceships or flash-bang rabbits-out-of-a-hat special effects. But the slow build has the effect of convincing us in our belief that it really did happen as narrated by our reluctant hero.
The 'What If?' is developed as it should be, and we are left with the satisfaction of a good SF tale well told. It deserves its status as an SF Master-work.