Does he actually, or is it just the classic SJW deception where somebody decides to not prostrate themselves and apologies profusely for some shit they never did, thus they're literally Hitler? The original sin that can never be cleansed despite how much you vainly do to make it right, which is the easiest scam - demand reparations then say it's not enough.
Considering the themes of his writing, I doubt he supports any side he just thinks people whining about the past need to shut the fuck up. That's why he's constantly talking about babies, children, the right to life - even the offspring of literal flesh demons with magic links to living weapons still aren't culpable for the actual events of those before them, they "don't know a thing".
Marley literally represents the hypocrisy of literal retards who whine about atrocities of the past whilst simultaneously helping themselves to all the nice things the "oppressors" gave them. When shit goes wrong and said whiners fuck something up, they can blame someone else because it's "the jews" or "the whites" or "the palestians" or of course "the japanese". There's no way Isayama isn't aware of all this shit beyond just Japan and Europe's 20th century politics.
Isayama is literally beyond woke. He's not just saying "we all need to get along" or "there are two sides" he's pointing out that children are free of any blame, and that people who indulge in self-loathing are the most pathetic, loathsome people on the planet.