One thing that has always bothered me is that the first series clearly showed that the Earth Kingdom was decentralized enough to survive years, if not decades, with minimal help from the "capital", and even other cities had other kings. It makes no sense that the kingdom would fall into such chaos after the assassination of the monarch in the "capital".
Those smaller satellite cities might be relatively autonomous but if the big guy in charge just got taken out, now it's fair game to take power for yourself.
I can imagine that realistically many provinces would try to become independent after the war, and centralization could come from crushing those rebellions, but that is not what the story shows.