The great diaspora

It started with the destruction of Ishamaltal's “tree of origin”, which was literally and symbolically the start of the collapse of many civilizations. Across Eden, the empires and kingdoms either experienced a crisis or a complete catastrophe, and many of them fractured or were even destroyed as a result.
The Ishtamal empire was the first, as its landscape changed from grass fields to an icy hellscape, causing many native and integrated races of the empire to flee into the highlands. 
The highland empire, already struggling with the unprecedented wave of refugees and the nobles pressuring king Midas for solutions, faced even more refugees in the south, as the Palma region was being decimated by a never before seen dragon. Panic ensued and the demands of the nobles grew more unreasonable, thus creating a split across the region between territories controlled by many different nobles, with some creating their own kingdom. There were those from both Palma and Ishmatal that immigrated to the lands of Anersha in search of a better life
Agera didn't experience a crisis like Kacera, but tensions reached the boiling point as the economy crashed in the Vinyan empire. As the economy was strained, the destruction of Desimir and sandworm attacks in the Sepheris desert freezing the markets completely collapsed their economy, ensuing panic among the nobles, the king, and the populace. Many fled to places like Xendir or Castilia.
In Sepheris, the desert faced a sudden increase in attacks by sandworms (many speculate the destruction of the tree that caused this), which led to a few towns being completely destroyed, and the kingdom of Shall Varok had to dedicate resources to not only combat the worms, but the different factions breaking off from the kingdom. The Shen Hi Kingdom was relatively unfazed by the collapse, but the intake of immigrants had caused problems as dealing with that many people was difficult.