@Academia Nut I think I know what happened to the Hathatyn. They had started some sort of forestry project (possibly turning forest into vineyards) when the drought hit. Without our irrigation or Black Soil, them messing with the forest caused the soil to critically weaken and their trees to dry out. After that, all it took was one spark. A massive wildfire swept their hills, causing devastation and panic. Just when that had passed though, the burned out debris caused debris flows (Landslides triggered by the weight of burned trees). They might have survived that, though it wouldn't have been pretty, but then they got hit by a third disaster: Floods. The debris blocked the natural waterpaths from the snowy mountains, especially that main river that they would have naturally built near. All of a sudden, their cities and fields were becoming lakes, causing mass displacement and starvation, and leaving only their worst farmland to try to feed people. And then, just to cap it off, they would have been hit by
yet another round of mudslides as the root system that was left rotted and got waterlogged from the flooding, sending even more mud cascades into the valleys. Worse, if they don't move
right now, they're in for a nasty round of diseases as that whole mess rots and breeds vermin, mold, and bacteria.
TL;DR: Nature's a
biiiiiitch.