Russian Civil War and associated conflicts such as the Polish-Soviet War
even some WWII fronts are underrepresented I think
A lot of WW2 games are either very large scale (all of the Pacific or all of Europe or fully Global) strategy games or really American-centric. Like a lot of North Africa, then Sicily, then Italy, then Normandy, now Battle of the Bulge things and little Eastern Front. Or even Western front before American involvement outside of maybe El-Alamein and Stalingrad.