The Best Years of Our Lives (1946) - follows American soldiers returning to society in the aftermath of WWII
Le silence de la mer (1949) - JP Melville's minimalist debut film about a Nazi officer that comes to a small French village. An excellent example of rogue independent filmmaking. Also see his take on the French Resistance in L'armée des ombre (1969)
Some that I haven't seen yet but probably qualify - J'accuse, Doctor Zhivago, Gods and Generals, Human Condition trilogy
I would also like to watch more Russian war films in general.
And some obvious ones for the sake of completeness - The Deer Hunter, Casablanca (even if it's a tad overrated), The Third Man, Ivan's Childhood, All Quiet on the Western Front, Paths of Glory