The Sundering

At the climax of The Primordial War, the forces of the Gods were overrun. The demonic armies swept across the lands of the human Kingdoms, massacring the population - men, women and children. The Gods did not have the strength of arms to rout or divert the invaders, and in their desperation they used powerful magic to crack the earth, in a cataclysm which would become known as the Sundering.
The Gods tore the continent in half. The ocean rushed in through the fissure, completely submerging the old kingdoms of men, forming the Sundered Sea. The majority of the Primordials army was drowned in a single moment, only a small vanguard contingent in the Elven Kingdoms of Athenon was spared, but they were now cut off from the conflict by the newly formed northern channel - the Wyrmscar.
The cost to the mortal forces was also high. It is estimated that more than three quarters of humanity drowned during the cataclysm, and many more died of starvation or exposure in the aftermath.