When Malefor came to rise, it isn’t clear what unbalanced things. The Kurosian race was on the decline, with Arkeyans and other races somehow overpowering smaller settlements among the mountains for thousands of years. Slowly over those years, the Kuros grew more desperate and confused, retreating back to the birthplace of their race; the Kurosian capital hidden behind the Veil.
It’s possible that Malefor was always meant for darkness, to help the Kuros regain their stance, or maybe he was suppost to wipe them out. Maybe it had nothing to do with the Kuros at all, and there was, and possibly is, something else disturbing the balance. Maybe Malefor either screwed things up more, or was right about bringing an age of destruction and rebirth.
Who knows! ;D
~Weird Hyenas