The Guns of the South — Harry Turtledove

January 1864-General Robert E. Lee faces defeat. The Army of Northern Virginia is ragged and ill-equipped. Gettysburg has broken the back of the Confederacy and decimated its manpower.

Then Andries Rhoodie, a strange man with an unplaceable accent, approaches Lee with an extraordinary offer. Rhoodie demonstrates an amazing rifle: its rate of fire is incredible, its lethal efficiency breathtaking--and Rhoodie guarantees unlimited quantities to the Confederates.

The name of the weapon is the AK-47...