Ah yes war crimes In a fantasy based RPG game Manga about medieval fuedal society with mechs. You're seriously trying to bring 21st century concepts into this xD forgetting the fact that the principality used what would be akin to weopons of mass destruction. Sureee buddy
Kingdom also isn't good guys never was that's kinda the whole point there
There are no real good guys.
As for your point about rebuilding i don't think you know history really well. Please tell me the last time a significantly smaller force that got completely decimated came back to beat the bigger enemy even if absorbed into a larger power (which wouldn't realistically happen in any given scenario here) as for small militia's they'd be annoying sure but it's not anything the kingdom would worry significantly about a well organised military is much more dangerous than unorganised rabble that'll slowly die out.
Saying it's better for both sides to be at peace makes it seem like both need to be at peace only one needs to be at peace the other just prefers it.
As for the killing all principality members. Literally no one is saying that but you xD. My main point is the principality can't really do anything about they girl getting hit even if they wanted to show outrage if the kingdom said "tough deal with it" it's not like they can do anything. Sure they'd be pissed about it but it's not like they'd be any more pissed than they already are literally that's the whole point about autonomous regions they almost always want to eventually achieve independence. You can argue diplomacy sure but the kingdom didn't exactly take their succession diplomatically the first time did they?
If Leon wants to rebel he would rebel anyways the kingdom doesn't exactly see eye to eye with him hell he barely tolerates it anyways and just uses it as a means to an end.
TLDR: you really used modern day political morality to talk about a manga based on bishoujo games xD
Are you dense, dumb, or didn't read the story? To completely give you a reminder: the otome game world isn't actually a world revolving around being an otome game. Thats the twist: everything happens to perfectly look like an otome game world to those who don't know better and are in the right place at the right time
The whole reason why its seen as an otome game is because people who got isekai into it play through Olivia's perspective, and from her pov, it's seen very much like an otome game. But things outside of her knowledge exist, LITERALLY LUXION AND THE WHOLE WAR AGAINST NEW HUMANS for example, or even the foundation for the nobility system for federal lord, which remind you anything about nobility/politics is literally outside of Olivia's pov, and that is especially a top secret for the highest ranking of nobility among the kingdom.
And to remind you again because you clearly are ignorant, willfully or not, the Queen trying to change the system with her long term plan already set in motion and is shown time and time again to be a kind person who wants things for the better but knows how to put her foot down. The Queen going to the academy only to see just how cruel it is, apologizing to Angelica and Leon, getting pissed off at Julius every time he does his dumb childish behaviors not realizing the weight of his actions, seeing through Marie BS, telling Hertrude the truth between the kingdom and principality, even bowing her head to the floor when asking Leon for help with Julius. The Queen
herself even speaks of ill of the bad things the kingdom has done, not to mention her conversation with Hertrude is literally the story itself explaining how the principality is the evil one and started the fights of the two nations. Literally making your "there are no good guys" comment look like some edgy writer seeing themselves as an intellectual thinking a grey world where everyone is the bad guys is a better story. Well guess what? There clearly is a good guy, the kingdom, and even with a rough past they are still the good days in the present.
I bring 21st century concepts like war crimes here because you are clearly too dumb to understand why people don't willfully do all those and need someone to dumb it down for you. People don't want to do things like a war crime because they see it as cruel. You don't go outside and see people play "kick the stray newborn puppy" as a sport every day because people see it as cruel and something you shouldn't do.
And you wanna know why Leon doesn't actually do anything he wants like rebel? Because he has a conscious. Take Leon's refusal to kill up until the war. The story spoon feeds you that he doesn't
want to kill. He tolerates the kingdom and doesn't take it over because there's actual good people like the Queen ruling it and its not his business to tell them what to do. And you missed the whole point of what I said being that why would people want to follow a warmonger leader who wants to kill oh a whim
If you are actually too dumb to understand anything happening in the story, despite the story telling the audience in pretty obvious ways, go back to reading edgy mangas with people constantly killing for no real reason other than shock value. And if you are smart enough re-read the manga parts you aren't understanding