@Fuew12
The issue is that all of what you say will just postpone things, and maybe not even for long. Sure, now the Amidonians prefer to eat ... but in a generation or less ( maybe even a year or two ), they will remember the dead ones of the war, the fact they are still exiled in the mountains and that the Kingdom still helds their ancestral lands. It is as certain as the sunrise that they will get or elect a belicose leadership that will repeat the invasions ... and given that the Kingdom has enemies, they will surely not lack support for that ( in fact foreign forces might just exarcebate things to cause a distraction ).
In other words , our isekai king just dropped a ticking bomb to whoever rules the Kingdom in a decade or two, just to get the issue out of the way for now ... or atleast that is what would happen if this was a realistic scenario ( because isekai kings tend to be Karma houdinis and escape the consequences of their sortsightness :/ ).