I show Spartacus every year whenever I teach world history. I show this film because there so few content appropriate movies that I can show that are anywhere near the actual history.
But I also show "The Devil's Brigade" with William Holden for WWII and "The Green Berets" with John Wayne for Vietnam. In none of these cases are my liberal fellow teachers very pleased. They don't like Spartacus because it shows slaves rising up with violence against their masters and to them violence under any circumstances is a B-A-D thing. The John Wayne film especially turns their stomachs.
If I were still teaching, and wanted to show a movie about the war in Vietnam, I don't know what I'd do. I don't think there are any particularly accurate movies about that war. The Deer Hunter is the great masterpiece to come out of that war, and while John Ford would likely have approved of it, had he lived to see it, it is more a work of poetry than history. As for WWII, based on my late uncle, who served in WWII and Korea, and who used to speak of the tedium, I would think that the one movie that best captured what those servicemen who survived the war experienced, would be Mister Roberts.