History of the World

The slaying of the Evil god Tiamat, one of the two creators of the world, was an incredibly massive change in the world. Tiamat was slayed by the combined efforts of all the races of the world, as well as by efforts of the gods of good. Bahamut dealt the killing blow, but all were involved.
After this event, evil continued. Evil gods existed, created by the evil races, but none were ever as powerful as Tiamat. As such, the world became a better place.
Some say that Tiamat wasnt killed, and some do still worship her, in secret, but these notions are misguided. The mental power required to create a new god is vast, and that to create a god on the scale of Tiamat would be worldchanging.