The whole country was made by the Gods as safe haven for people with magic power, i.e. the nobles in current time.
In the past the religion IS the core, even influencing the ruler, because through worship the nobles can gain blessings from the Gods which make their magic more powerful, and the most powerful of nobles is the one ruling as the "king" from the first temple and the land split into smaller sections for various Lords (who then split their domains into smaller areas for various smaller nobles)
(The title isn't "king" but I'll just use king for the sake of simplicity)
Then due to certain incident and over long period of time, the importance of the temple was forgotten and the old traditions lost.
The tl;dr is that traditionally you get a magic item as proof you've earned qualification for kingship, and the next king is chosen among the people who has this item.
Think of the magic circuit at the center of the country as a computer an the magic item is tablet for accessing various functions of it.
Then one queen who want her son to inherit the kingship, but the son wasn't strong enough to earn the item himself, make a magic tool that copy the important functions of the item and give her to her son, allowing him to inherit the title.
Then said son passed it down, etc etc. Eventually people forgot how to actually EARN said magic item.
So once it's lost in the recent coup....well, it's going downhill even if slowly.
And yes Myne will ends up embroiled in those stuffs, more often than not caused by her desire for books.
(seriously, her accidentally starting the path towards that magic item was because she just wanted to enter a SECRET LIBRARY.......)