When we talk with people, especially people who aren't grounded in the science fictional and the fantastic, about Land of Mist and Snow, one question is almost certain to come up early in the conversation: Why write this kind of book--an alternate-historical fantasy novel--about something as real and as central to the American experience as the Civil War?
Straight alternate history is a recognized subgenre of science fiction; in the guise of counterfactual history it even has a modicum of academic respectability. Why, then, do we need to add fantasy to the mix as well?
Leaving aside the obvious answer ("because that was the way the story came to us asking to be told"), there are several good reasons for choosing to employ fantasy as our fictional medium. First, because there was in fact no pressing reason not to write the story as a fantasy. Before the modern novel, with its demands for mimetic realism and psychological verisimilitude, came to dominate the literary landscape, fantasy was a respectable and legitimate medium for serious literary undertakings. Spenser certainly thought so when he wrote The Faerie Queene,and Swift when he wrote Gulliver's Travels.
For another thing, when it comes to dealing with large important issues (things like slavery and freedom, for instance) fantasy has some advantages that realism doesn't. Fantasy is the genre in which metaphors and symbols can be given life and physical existence. Instead of dealing with ideals and abstractions at one remove, the writer can introduce them directly into the tale as independent actors. And issues in this country don't come much larger or more important than the Civil War.
If the stories and legends of King Arthur make up the Matter of Britain, and those of Charlemagne the Matter of France, then the Civil War is surely the heart of the Matter of America: It is the painful working-out in blood of the original sin of the Republic, the failure to deal with the problem of slavery; and the resolution by force of arms of the contradictory existence of sovereign states inside a sovereign nation. Moreover, the Civil War is rife with the sort of incidents that would pass as folklore if they were not true--such as (to pick only one) the way that it began on Wilmer McLean's plantation in Manassas, Virginia, with the First Battle of Bull Run, and ended four years later with Lee's surrender to Grant in McLean's home at Appomattox Court House. You couldn't possibly make something like that up and have it feel like stark realism.
So in a way we merely followed the path of least resistance in setting Land of Mist and Snow in a milieu where the supernatural and the numinous are both present and manipulable, and where liberty, oppression, and union can escape from the bonds of symbolism and allegory to run free through the wilderness of plot.