Cassutt, Michael. "Mules in Horses' Harness"
Divergence: 1863 CE
What if: Lincoln was assassinated while visiting a Union hospital on July 4, 1863. Wasn't he?
Summary: 1980 Confederate differential engineers trying to model history explore the Great Man hypothesis.
Published: In What Might Have Been? Volume 2: Alternate Heroes (eds. Gregory Benford and Martin H. Greenberg), q.v.