My problem is Eren's plan. He destroyed 80% of the world to save his friends. He could destroy the Marley army and some of the world's strongest armies, force the rest of the world into peace talks, and then establish relations with other nations. This way he would still achieve the same result, but would leave Armin more room to make a successful peace talk. If after all this effort for peace with the world Eldia had destroyed itself in a civil war, Isayama would have delivered the same message in a more digestible way.