It is deeply humanistic in its argument that at heart the soldiers on opposing sides of the war shared similar fears and hopes, which in its own way underpins the argument for robust jus in bello. But, and I think Eastwood acknowledges this, understanding the enemy has very little to do with the decision to go to war in the first place (jus ad bellum). The film is decontextualized: while it hints at oppression in Imperial Japan through the story of Shimizu, the disgraced Kempeitai trooper, there is little suggestion of the atrocities committed by the Imperial Japanese Army against Asian peoples and Allied soldiers or of Japanese aggression in general. While decontextualizing the story of the defense of Iwo Jima makes for a more moving film, it also means ignoring the larger questions of war and peace, the question of why the US and Japan came to blows in the first place. So while it is supremely valuable as a portrait of the Japanese war effort and infantrymen at war, it fails as a sophisticated account of the Pacific War.
That said, it is an extremely well-made and well-acted film.