@monkey123 Politically the MC's setup is very rushed. Let's take this scenario from the perspective of a duke:
1) King out of the blue appoints an unknown foreigner not of the dynasty as king
2) King subsequently disappears from public, never to be seen again. If that doesn't imply house arrest then I don't know what.
3) I'm not sure if the LN touches on this, but it doesn't seem like this is a matrilineal marriage. A new dynasty is in charge. All your political favors you curried with the previous dynasty? Gone.
4) Foreigner unilaterally appoints a bunch of unknown persons into his council, without consulting you, the Duke. There are literally no vassals on the council. For all intents and purpose, this is abolishing the power of the council to keep the king in check, for any feudal structure this is quite a big deal. It means the king can issue laws without vassals input.
5) Foreigner comes to you and demands you give up the right to organize military force in exchange for... nothing? Again, this breaks the feudal contract. That means you're going to be paying taxes AND levies without any gains. You don't even have any control over the use of the levies anymore.
6) He quotes some random passage about deposing tyrants, but how are you even going to depose him without your own military force (lol)
Now he's pulling a false flag and destroying infrastructure within his own territory, all while an advancing army is coming in. The important stuff like the wells seems to be still intact. The manga doesn't make it clear whose land the MC is doing this to, but if it's a count/baron vassal then that'll be double the tyranny. Imagine if you as a duke found out about that. Doesn't seem like a liege you would trust.
I have a feeling the author is confusing the feudal system with imperial bureaucracies. MC isn't the Yellow Emperor, feudal kings can't strip people of power overtly like this without expecting huge backlash. I understand his need for centralization, but that is something you need to do slowly and covertly in this case. Taking a bunch of steps that basically ensure a civil war while you know external kingdoms have a claim on your land and are eager to take advantage of your position also seems... unwise.