The rise of Li'sleith

Geological / environmental event

As the gods cultivated and refined magic a third world tree rose from the waters and strengthened not only the divine connection to magic but also gave the breath of magic to any of the mortal races that lived under her. From this the elves most in tune with magic summoned beings from other planes. These beings, who were already at war with eachother from before being summoned, enslaved the elves in an attempt to win the war and thus taught them both good and evil. In many cases this enslavement led to children of mixed blood, about the same strength as the elves but with unique features from their otherworld parents.