Rulers of Darkness by Harry Turtledove

The author of the Worldwar and Great War series displays his virtuoso command of the details of WWII in this fourth book (after 2001's Through the Darkness) about a conflict between mythical feudal kingdoms using magic instead of science as the basis for technology. Aficionados will enjoy picking out the parallels the Japan-analog Gyonghos Empire, for example, fights "the grinning dwarves of Kuusamo" (i.e., the United States). On the equivalent of the Eastern front, the German-based Algarvian Empire recovers from its losses in the frozen urban hell of Sulingen and prepares for its usual summer advance against the forces of King Swemmel of Unkerlant, leading to a replay of the battle of Kursk. Turtledove's great strength has always been the depiction of ordinary characters who have to live with the consequences of their superiors' decisions an Algarvian policeman in Forthweg objects to rounding up Kaunians, while a group of theoretical magicians must work on a thaumaturgical Manhattan Project.