Duck Soup (1933)

Groucho Marx is made leader of bankrupt Freedonia and talks his way into a war with neighbouring Sylvania, largely because it would be rude not to. The target is the whole apparatus of nationalism: anthems, ultimatums, ambassadors and the pomp that turns a personal insult into a casus belli. No background needed beyond knowing that Europe in 1933 was rearming. The mirror routine and the war-declaring musical number are as fast and strange as anything made since, and at around 70 minutes it is the shortest route into the genre.