The Guns of the South
Turtledove, Harry. The Guns of the South: A Novel of the Civil War. New York: Ballantine, 1992.
The War takes a turn in favor of the Confederacy when a small group of South African time-travelers arrives from the 21st century bearing AK-47s for Robert E. Lee's beleaguered army.
Turtledove's energetic speculation, a fan favorite, has flashes of interest, but founders in trying to flesh its bizarre premise into an epic novel of alternative history.