Effinger is a Northerner who, at the time of writing this book, had been living in New Orleans for about 20 years. So he sees the American Civil War (or the War of Northern Aggression) from both sides now. This is his novella about it.
Our viewpoint characters are a young soldier and a boy, who wander through the battle for Atlanta. We see the idiocy of war, the random violence of it, and the squalor. We also get the viewpoint from both sides, as the young soldier is a Yankee and many of those he encounters are Southerners.
Effinger is a science fiction and fantasy writer, but I didn't see any fantasy here. He's writing a fictional story set during the war, focusing on some of the well-known (and lesser known) idiocies of the war.
It's an entertaining read and short, at 74 pages not including the introduction by Gregory Benford or the author's postscript. My major criticism is that I found the voice of the boy a little more mature and worldly-wise than it should be (but then perhaps he's not a real person, but an archetype. There's the possible fantasy elements for you.)
This short book was published in only 900 copies, so you won't get it from a library. But it seems to be available from the usual online book sources.