Maybe the most striking bit of its exploration of the morality of war is that the series spends something like 45 books building up the alien Andalites as beneficent do-gooders who the team of protagonists expect to swoop in and fix everything (including one of the protagonists who is a young Andalite stranded on Earth), and then it turns out that they've been as morally worn down by the ongoing interstellar war as the protagonists have in their guerrilla conflicts on Earth and are effectively as hostile to humans as the original invaders.
