chilliout people its only 18 chapters, most mangas are shitty the first dozen of chaps. At least the whole history/economic lesson its kinda entertaining.
@Revassin i think almost all mangas are taken from the Light Novel edition which its usually "better" written since they have an actual editor now, sometimes they add stuff while keeping the story mostly the same, or change it almost entirely (Shield Bro comes to mind)
All the nobles basically colluded to install the second prince as the king or they would defect to another nation, making the current king essentially powerless. Not that hard nor simple to comprehend, just need to read between the lines i guess.