The Sundering was the catastrophic civil war that tore the elven race asunder and forever divided the High Elves from the Dark Elves. It arose from the machinations of Malekith, son of the first Phoenix King, who plunged the island-realm of Ulthuan into ruin when he was passed over for the throne and turned to the worship of the Dark Gods.
The war raged for centuries, brother slaying brother across the fair lands of Ulthuan. In its final convulsion, Malekith and his mother Morathi attempted to seize the vortex that drains Chaos magic from the world; the resulting cataclysm shattered the continent, sinking whole kingdoms beneath the waves and drowning countless thousands. Defeated, the followers of Malekith fled across the ocean to the cold land of Naggaroth, becoming the Dark Elves.
The Sundering left a wound in the elven soul that has never healed. From that day, the sundered kindreds have waged an unending war of vengeance and hatred, each convinced of its rightful claim to the legacy of the elder race.