The war between Bahamut and Tiamat.
After the divide between the Church of the Dragon, Bahamut led his followers to further prosperity in his lands. But Tiamat had schemed for a long time, and her followers had become evil shadows of their former selves. Still holding the long grudge against Bahamut, she unleashed a vengeant wave of darkness from the east, and her forces invaded the west. But Tiamat underestimated the Platinum Army, and a terrible war started would go on to rage for two thousand years, completely exhausting and eradicating most of the dwarven lands, known today as the Dwarven Barrens, as well as large parts of the eastern lands. During the war, Odari attempted to intervene in order to stop it. He sent his Knights of Val to interfere in the holy war, and threatened to eradicate both sides. Bahamut and Tiamat, somehow, struck at the same time at the Valheim mountain, cutting off the source of power for the Knights of Val, and they were soundly defeated. Billions of mortals and dragons died in the war and even our beloved Bahamut gave his life, but their sacrifice was not in vain. For Tiamat was cast out of the mortal realm, her terrible miasmic body corrupting the entire eastern lands. To ensure that the same would never again happen, Bahamut rose a mountainrange to seal off the eastern lands, and constructed a wall that would scale the entire mountainrange, called the Barrier. The Barrier is a testament to Bahamut's power and benevolence, and serves as the first line of defense against the forces of darkness.