Ancestors of Mia and the rest of Tearmoon's nobles were invaders. The first emperor made an agreement with a doomsday cult that in exchange of their help, the king would build a contradiction in the empire that despite the fact that the land is very fertile, the nobles would be encouraged to pursue activities other than farming. This obviously will cause the empire to self destruct later during the time of famine, as the empire won't have enough food to feed itself and it would cause rebellion, chaos, and destruction, which what happened in Mia's original timeline. In the end, Mia managed to avert the destruction in her timeline, but it instead would happen in her granddaughter's timeline.
And the chaos would spread all over the world. which is basically the goal of the cult, to bring destruction to the world, so a better world would emerge from the ashes.