There's a tendency to assume that the only way that war (or, more accurately, anti-war) films can be effective is to show the horror of battle in all its gruesome detail: hence Apocalypse Now and the stunning opening to Saving Private Ryan. Only rarely, then, do we see an effective anti-war animation.
Grave Of The Fireflies is the first Japanese animation I've seen that's not directed by Miyazaki. I chose this because it's in the IMDb top 200 (#163 at the moment; Princess Mononoke is at #100, Spirited Away at a scarcely believable #41).
Fireflies is an excellent film, but a long way removed from the fantasy worlds of Miyazaki and is certainly not a children's film, despite being about two children. It's set during the final months of the Second World War and concerns a young boy, orphaned by the US firebombing of his city, as he misguidedly struggles to look after his four-year-old sister. With the film told in flashback, from the very first scene, we know it's not going to end well, as we see him die emaciated and alone in a subway just after the end of war.
The fireflies of the title feature in both a literal and figurative sense; fireflies being, as we are told, creatures that burn brightly and die too soon. It's powerful and horrifying material, definitely not the sort of thing one expects to see in an animation of any kind. In its analysis of the effects of conflict on the civilian population in general, and innocent children in particular, it turns out to be a potent anti-war film, as well as an intimate portrait of sibling love. Where once I described Life Is Beautiful as a comedy version of Schindler's List, I can now only describe Grave Of The Fireflies as a tragic version of Life Is Beautiful as the boy struggles and ultimately fails to protect his sister from the true horrors of war. In mood, the film closely resembles Raymond Briggs' When The Wind Blows. That, too, concerns two innocents - in this case, an elderly couple - failing to cope with the war being waged around them.
It's also allegorical inasmuch as the boy's blundering attempts to protect his sister are increasingly desperate, mirroring the misplaced arrogance of the Japanese military in their increasingly evidently futile attempts to win the war. Plus it is, of course, as beautifully drawn as any Ghibli film.
As devastating an anti-war poem as one could wish for, this is an essential part of my DVD collection, despite the fact that I can scarcely bear to watch it again. Recommended, but for when one is in a sombre mood.