Well, lots of Hollywood films from 1940 wrestle with the problem of the wars that were then raging in Asia and Europe, and with the likelihood that the US couldn't keep itself out of the madness for very much longer. And this is a pretty blatant example; set just before the Civil War that all the characters "know" to be coming, with every other person making statements about how they're not going to start making moral decisions because they're soldiers who just do their duty. So the film has acquired an interesting historical patina. But the subject matter is just so toe-curlingly awful that there ought to be a health warning before it's shown. Perhaps its best audience would be students of history-with-ethics. And if there's no such college course, perhaps it's best not viewed at all. Plenty of other films to watch, with Errol and Olivia and gunfights (or bowfights)!
Review of Santa Fe Trail
