Alternate history novels, if well written, can teach you a lot about real history, too. The idea is to change one event, and examine the repercussions. That provides a means to examine the social and political issues of the time in a fresh light. In the American Civil War you can discuss slavery and the South's class system, in early America you can discuss the problems of Native Americans . Reading an alternate history novel often prompts me to research the real events and issues, and once I've done so, the novel becomes much more rich and realistic.
L. Sprague De Camp's seminal Lest Darkness Fall1 is an excellent example of the AH novel. It is a very entertaining read, buttressed by solid research and painstaking attention to historical accuracy. Lest Darkness Fall is filled with minutiae about the life of the common man in sixth century Rome (aka the Byzantine Empire). The Byzantine Empire is also a favo(u)rite stomping grounds for prolific AH author Harry Turtledove.
According to the Ancient History section of about.com, Harry Turtledove himself tells us that the first alternate history was written by Livy, who asked what would have happened if Alexander the Great had turned west to attack Rome, instead of east to Persia.
- It should be noted that the plot of "Lest Darkness Fall" closely parallels Mark Twain's "A Connecticut Yankee in King Arthur's Court", but De Camp's keen attention to historical accuracy while maintaining a great yarn made the book a prototype for all that would come after.