The situation described in chapter 59 is starting to happen: Treia took in too much land and population (100,000 people while they themselves only had a population of 300,000) from the former Gordonia kingdom.
This land was devastated by the war and the population impoverished, which means it’s Treia would need to heavily invest in rebuilding it while getting almost no taxes. As the territory and population they took in amounts to a quarter of their total population, there is no way Treia can finance this and is forced to raise taxes. This in turn will lead to unrest, meaning even less tax money, and turn into a downward spiral.