Moffett, Judith. "Chickasaw Slave"
Divergence: 1828 CE
What if: Andrew Jackson's image was tarnished by a land-dealing scandal, leading to Davey Crockett becoming president in 1828.
Summary: Just as the Confederacy wins its independence in 1853, a soldier recounts how the flight of a slave may have broken the Compromise of 1850.
Published: In Isaac Asimov's Science Fiction Magazine, September 1991; and Alternate Presidents (ed. Mike Resnick), q.v.