The Deep Ones broke the Arm of Dorne and caused The Doom of Valyria

[DragonSnow]

Background

Black Stones: http://awoiaf.westeros.org/index.php/Black_stone

So we know there are mysterious oily black stones scattered across The Known World. Seastone Chair on the Iron Islands, 40 ft statue of a Toad on Isle of Toads, Buildings in Asshai. All located near the Sea.

These black stones are similar but different from the black stone on the foundation of Hightower at Oldtown and the Five Forts in Yi Ti and the remaining Valyrian dragonfire structures. These stone are the same in every way except they are not described as oily but rather as fused black stone.

Bloodstone Emperor: http://awoiaf.westeros.org/index.php/Bloodstone_Emperor

The last emperor of the old Yi Ti emperor. This guy killed his sister. Married a "tiger women" and was so bad his actions are blamed for the coming of the Long Night. But importantly upon his ascension to the Yi Ti thrown he cast down the true gods of Yi Ti, to worship a black stone that fell from the sky. He founded the Church of Starry Wisdom which is still practiced today in some port cities

Deep Ones: http://awoiaf.westeros.org/index.php/Deep_Ones

The black stones are associated with what's known as the Deep Ones (a fabled mythical race of half men half sea creature). I am assuming that The Drowned God of the Iron Islands, the Old Ones of Ling, the Rhoynish Gods known as Mother Rhoyne and Old Men of the River, and the Gods of The Thousand Islands are all the references to the same entity or entities under the sea.

Patchface: http://awoiaf.westeros.org/index.php/Patchface

Patchface supposedly met the deep ones and now sings cryptic tales of something in the sea that will eventually rise out of the water. He is currently a jester at Dragonstone

Mazemakers of Lorath: http://awoiaf.westeros.org/index.php/Mazemakers

The legends of the Lorathi state the mazemakers were destroyed by creatures of the sea, such as merlings, selkies, or walrus-men. Lorath is a city next to the sea.

So I am of the belief that there is a race of underwater dwellers have are as old or older than The Children and Giants. I also believe that the Deep Ones are responsible for submerging the land bridge between Westeros and Essos. The Children had a hand in it but the Deep Ones did the heavy lifting.

Additionally, the Deep Ones are responsible for the Doom of Valyria. Valyria was a coastal city and considering that nearly all the dragonlords and dragons were in Valyria during the doom the timing can’t be a coincidence. The Doom occurred partly as revenge for the Valyrians wiping out the 250,000 strong army of Rhoynar. The surviving Rhoynars who didn’t leave on the 10,000 ships abandoned their old religion worshipping the gods of the river after defeat for the Faith of the Seven. Also, assuming the Deep Ones have long planned on returning to the surface to rule once again it would make sense to destroy the greatest threat to their rule. (The Valyrians have so many dragons at the time they could make huge bodies of water boil)

The Deep Ones are the lost race that ruled the world before the rise of mankind. The Deep Ones have teamed up with The Children who are tired of living on the fringes and want to reclaim their old turf in Westeros. The Deep Ones will probably have some of mankind on their side. The Ironborn for example I assume will side with The Deep Ones. Bloodraven maybe also aware of the Deep Ones and is helping them. Members of the Church of Starry Wisdom are all for the take over. Some forces in Assahai probably will have a hand in the Deep Ones reemergence.

So how will a majority of mankind fight such a powerful foe?

We will not see the White Walkers and the Dragons battle it out. Instead they will both have to join forces to defeat the Deep Ones once and for all. I believe that the events for the Long Night have been misinterpreted over the centuries and the White Walkers got cast as the bad guys but in reality they fight alongside mankind. The current White Walkers are gearing up for the fight. They know what is coming.

Perhaps the known world like Earth was once completed covered in water and only after land masses began to rise out of the water did The Great Ones lose their grip on control of the world.

What do you think?

[TheGreatestOther]

I like your theory having the others cast as the big bads of the story but in reality the deep ones are the big bads. Only problem i have is the story is called a song of ice and fire not a song of ice fire and water doesn't make as much sense for the final battle to be fire and ice teaming up to defeat water but I could see the deep ones joining a side.