Cover art
Chalker, Jack L. Downtiming the Night Side. Baen 1993.

Chalker, Jack L. Downtiming the Night Side
Divergence: 1841 CE
What if: Karl Marx died in 1841, causing Russia to become a weak democracy in 1917 and thus unable to fend off Germany in 1941.
Summary: A security officer on a time travel project chases terrorists back to 1841 and gets lost in a timewar between Earthers and Offworlders.
Published: Tor 1985 (0812532880), Baen 1993 (0671721704w88 android).