Len Deighton wrote several books set in and around on WW2 - all are pretty good.
For an interesting alternative, try his SS-GB - a murder mystery set in England after the Germans have successfully invaded and conquered the island. Since the case eventually involves the highest levels of all major nations that were involved in WW2, it explores many ‘what-ifs’ regarding alliances, balance of power, governments etc.
I don’t know if John Buchan’s books of WW1 qualify as historical novels, since they were written during the war itself. Greenmantle was published in 1916 and Mr. Standfast in 1918. Around 1/3 of Greenmantle is set in Germany, and much of the 2nd half of Mr. Standfast is set in France.
The Project Gutenberg eBook of Greenmantle, by John Buchan
Mr. Standfast, by John Buchan (gutenberg.org)
And seconding the recommendation for Irene Nemirovski’s Suite Francaise.