Doom of Valyria

The Doom of Valyria was a catastrophic event that took place nearly four hundred years before the events of Game of Thrones. It caused the fall of the Valyrian Freehold and would lead, indirectly, to the conquest of the Seven Kingdoms of Westeros by House Targaryen. For nearly five thousand years, the Valyrian Freehold had remained the dominant power in the continent of Essos, thanks to the dragons, mighty beasts that were key to their power. The nature of the Doom remains unknown, while some believe it was a massive volcanic eruption of the Fourteen Fires, others believe it was the result of the Valyrians' own sorcery. Whatever the cause, "the Doom", as it became known, laid waste to the Valyrian capital, its people, and the surrounding lands.

The Valyrian peninsula itself was shattered and the ocean came sweeping in, becoming the area now known as the Smoking Sea - which no sailor may dare cross and which is said to be haunted by demons. All dragons were thought to be lost, as well as all Valyrian recorded history, spells, and knowledge. With its center of power destroyed, the Freehold collapsed. And of the mighty families of dragonlords who ruled the Freehold, only one survived, House Targaryen, which had established on Dragonstone years before the Doom.