I don’t know if it counts as a war movie but the 1977 version of The Four Feathers has one of the best battle scenes I’ve ever seen in a movie. Impressively well-done for a made-for-TV movie.
Odd how the US fought what are called the “Banana Wars” from 1898 to 1934, with more casualites than the US Civil War (mostly Filipinos), and the only two movies I can think of are the terribly innacurate The Real Glory, a Gary Cooper flag-waver, and a turgidly philisophical Gary Cooper in They Came to Cordura (which added Dick York to the casualty list. He broke his back in the battle scene and eventually Bewitched replaced his comically neurotic Darin with Dick Sergeant’s grouchy WASP asshole Darin.)
Best War Movie? How about the USSR’s 1965 War and Peace? cost almost a billion dollars in 2010 money. Had a good writer, too.
Dammit, spoke-, that’s the one I came in here to mention. Just saw this on a pristine Criterion release; incredibly affecting wartime drama that takes place during the war that begat Memorial Day (the Civil War). Oddly, the summary offered by Wikipedia seems to downplay the Lawrence Massacre that is a central plot point of the movie. And although it does focus on the relationships and friendships of the bushwhacker boys, there’s at least one big messy battlefield scene in addition to the many pillaging scenes.