The Corruption

The Corruption started when Vufex, the 'God of Chaos' became jealous of his siblings, especially those with far more prosperous lands. And particularly his sister Silva for creating the first ever example of 'magic'. As a result Vufex created his own, darker more powerful form of magic and cursed their lands which today is known as the taint. The corruption ended up spreading far beyond Vufex's control and as a result it wiped out the population of Utania.

The full history of Utania can be read on the Eras wiki page.