After a decisive victory at the battle of Arambar Gulch, the rebel dragonborn leaders Iskdara and Shurideh had gained a powerful artifact known as the Eye of Blazing Rorn, after felling its previous owner, the silver dragon Asativarainuth. The two dragonborn sisters joined forces with the leaders of other rebel war bands, in order to kill the most powerful of the dragon tyrants of Abeir, the red dragon Rhodrolytharnestrix.
They went to the Celestial Mountain, a dormant volcano where Rhodrolytharnestrix had his lair, and opened a tunnel to the lava chambers using the Breath of Petron. While the rest of the dragonborn leaders led their war bands against Rhodrolytharnestrix's dragon army, Iskara, Shurideh, Reshvemi, and Thuchir infiltrated the mountain and dropped the Eye of Blazing Rorn into the volcano, triggering an eruption so powerful that it killed Rhodrolytharnestrix, even though he was a red dragon.
The Celestial Mountain was destroyed, and was called the Crippled Mountain since then. The dragonborn heroes survived the explosion and reunited with the other rebel leaders, creating the dragonborn nation of Tymanchebar. The ash from the eruption fell for forty days, and the dragonborn began to call themselves the "vayemniri" (Ash-Marked Ones, in draconic), so that they would always remember the way they gained their freedom.
Although she tried her best, sending wave after wave of dragons to attack the dragonborn lands, the Empress Dragon Gauwervyndhal was unable to conquer Tymanchebar. This remained unchanged until the Blue Breath of Change transported Laerakond to the world of Toril.