As people perceive it:
Sometime, eons ago, the gods created the land and walked among the mountains and valleys. There were many gods, but the world is large, and the gods each chose areas to call their own, to cultivate and to create in. But some gods grew jealous of other gods and their lands and war began. Each of the gods sought to destroy the others, calling forth terrible creatures and powerful magics to rain death on their rivals. In time, the gods destroyed one another, until only one, the strongest of them all, survived. He withdrew from the world, but left the fell creatures and strange magics which distort the world.
As it really happened:
Eons ago, when the Exiles were first cast out of heaven for their rebellion, they lived in peace together. But as time went on, some sought power over other Exiles and some sought to rise up and assail the gates of Heaven and "take back what was theirs" while others remained content in their exile or chose to withdraw altogether. The Exiles drew forth terrible elemental creatures and conjured powerful magics - some with the intent to attack the Creator, others with the intent to quell this second rebellion. The rebellion was crushed and the twice rebellious Exiles who survived slunk off into darkened places to sulk in bitterness and hatch more plots. The Exiles who remained (largely in the northern reaches) could not undo much of the damage done by the rebellious Exiles, but continue to aid where they can. The monstrous creatures still roam the land and the powerful magics called forth warp the very fabric of reality.