Here are a few to add to the collective list. I am attempting to not be too repetitive.
-Casablanca
-Arch of Triumph
-Sink the Bismark
-Henry V: Prince Hal blows up the entire French Army on St. Crispin's Day in the year 1415 at the Battle of Agincourt. Shakespeare coined the term "We Band of Brothers" for use in Prince Hal's famous speech. If he had not coined this phrase, we would never have had the widely acclaimed TV miniseries.
-Braveheart: Mr. Gibson does an admirable job of recreating the Battle of Stirling Bridge, even though he leaves out the bridge, filming it simply as the Battle of Stirling. Here is an artist's depiction that I believe makes up partially for this dereliction. (He filmed the movie in Ireland and did not have access to a suitable bridge, or so the story goes.)
-The Good German: set in the aftermath of WWII Berlin and Potsdam, it deals mostly with hubris and confusion after the total destruction of Germany. Everyone is seeking to establish a new identity, by disavowing their wartime acts and activities. Animosity and suspicion is everywhere.
-The Book Thief
-The Killing Fields:
-Oppenheimer is a "best ever" in whatever sub-genre, you wish to place it.
-Master and Commander: Mentioned above
-Gone With the Wind; A superlative recreation of the era and of the aftermath of War - Scarlett O'Hara will remain as everyone's dream debutante for all time. Not even her namesake, Scarlett Johanson can come close. What a Woman, fictional or otherwise!
Several semi-obscure and "Not for everybody" war movies - "arthouse films" that are highly focused, narrow in scope but brilliantly done
-Richard III - a highly stylized Shakespearean masterpiece/Updated to include tanks, machine guns and open staff cars with motorcycle outriders.
-Seven Beauties (Lina Wertmuller) - hard to watch, not much is in good taste except perhaps the ultimate message
-The English Patient
-The Garden of the Finzi-Continis
-The Night Porter - provocative and problematic, very controversial / Charlotte Rampling and Dirk Bogarde