Hooo boy.
Yeah, while all you guys are all "FUCK YEAH! MC FOLLOWED THROUGH!", ya'll are forgetting that this country doesn't exist in a vacuum. There are other countries as well. And while none of them are as powerful?
Uh, yeah. This country just literally got decapitated. And in a way that the other, very important people (like the nobles who are responsible for defending their borders) are not gonna know about for a while. Granted, this also means that future invaders won't know until about the same time, but yeah, you get the idea.
Now.
I'm not saying this out of pity for the ruling class. I'm saying this because in settings like these? You deconstruct them even a little bit, and it becomes a charnel house of rape, murder, and pillaging.
I think the opening track for VNV Nation's album "Praise The Fallen" puts it best:
That. Exactly. That is the fate that awaits the people of this kingdom, who had fuck-and-all to do with the MC's pain and suffering.
If this is what comes to pass, then the MC is gonna find that he's done far worse to far more people that these ass hole rulers did.
And then his class mates are going to be perfectly justified in coming after his stupid revenge-happy ass.
After all, why do you think that demon had such a big grin on his face? It was not just the innocents in that castle. It's because the MC just bought this world an entire fucking Amazon Hub packed to the rafters with nothing but pain and suffering, wholesale, and he's passing the savings on to everyone else.
EDIT: Oh, and BTW? Where do you think this country's treasury was at?
Did anyone see a bunch of money at the bottom of this crater?
No?
Yeah. Guess what? He just fucking disappeared all of this country's funds.
Nice job breaking it, hero.