In 231 PK, the Black Fire War was raging between the tieflings and humans of Falwyth and the dragonborn of Azmartheon. On a day that was recorded as clear and cold, deep in the Keshwan winter, an event happened that forever changed the geography of the region.
Black storm clouds suddenly formed over Falwyth, sending acidic rains and smashing chunks of hail down upon them. At the same time, fires sprang from the ground in Azmartheon, and the soil, always so lush and full of life, turned born and dead, becoming rough sand that was whipped to scouring speeds by cyclones from the black sky. The ground cracked, and chunks of both kingdoms fell into the sea.
Suddenly, the very ground beneath Falwyth seemed to heave up in a terrible explosion, casting soldiers, civilians, and even whole towns sliding into waves that seemed suddenly full of darkness and blood. The cloud of dust hung in the sky over Azmartheon, choking the land until it could no longer support life. Grimly, the dragonborn abandoned their ancestral lands to become a race of wanderers.
When the clouds cleared, those who returned to explore found that all that was left of Falwyth was a broken, jagged archipelago, a few of which were capable of sustaining life. On some of these, tiefling tyrants created small, scheming kingdoms, insular and mysterious. Azmartheon was now only a desolation, unfit for civilized folk to inhabit.
No one knows what caused this event, which was termed The Rending. Both sides blame each other, but no one has ever offered definitive proof. The disaster remains a sad and painful mystery, its legacy a scar upon the land even some 1,300 years later.