Originally named Terrash the world that we live in is now a world of miles and miles of deep uninviting water but it was not always this way.
Five thousand years ago the world was a pretty peaceful place. There was small wars but the different races mostly lived in their own areas with very little interaction. Magic was an everyday tool for many of the people of Terrash, well for everyone but the humans who the gods had not seen fit to bestow magical energy to. A group of humans, named the Red Cloaks, banded together to change this. Led by a charismatic alchemist/scientist named Hallister.
Hallister and The Great War:
Hallister in his research had come across a way to steal magical energy directly from the world and the gods. He set his band of Red Cloaks to work. First creating the cavernous system of tunnels, caves, research labs, strongholds, and encampments under the town of waterdeep. Second was getting together test subjects, weapons, magical items, and elements needed to put his plan into action.
Hallister worked in his cave system, now known as Undermountain, for many years until the fateful day when he had enough magical energy to lead his army of Red Cloaks, and experiments into battle directly with the gods. The war lasted for 500 years with Hallister becoming more powerful with each passing year. The battles left heavy casualties on both sides Hallister lost many red cloaks and experiments and the gods lost a number of angels and followers and even a few of the gods themselves passed namely Deneir, Leira, and Chemosh.
The End of the Great War:
There was a great final battle on Terrash where the full force of both Hallister’s and the Gods armies met. The Battle lasted for over a year of back and forth with neither side relenting. The fighting was so fierce and constant that there was never a safe time to remove the bodies of loved ones or have funerals for the many fallen. The blood of both sides flowed in wide rivers some would pool into lakes. Bodies covered the battlefield like a carpet and still the fighting continued.
The stories of what ended the war diverge between the Hallister supporters and the religious sects.
The religious sects tell the story of Hallister, seeing that he was losing, came up with a plan to hold the world hostage by opening the portal to the water plane and flooding the world only stopping when the gods retreated. In their retreat the gods made a land mass, named Denoshire, for all the races of the world to live in peace.
The Hallister supporters say the gods were on the back foot, losing many and on the verge of either dying or being pushed from the physical plane altogether. Took a last ditch effort and opened up a portal to the Water Plane. When Hallister saw this he surrendered and used the last of his magical energy to raise a safe haven for all the races to live.
Either way during the flooding the Cave dwelling races started sealing up all but the highest of openings. Other races ran for the high ground. During the ensuing chaos the war stopped. Waterdeep and the surrounding area were raised up to create a valley surrounded by mountains. Other than this area the only lands left are the tops of old mountain ranges and some of the highest plateaus.
After the War:
Hallister and the few red cloaks who survived the battle were not heard from again after that final battle. The entrances to Undermountain were sealed and lost to time. The gods who had such a large hand in the world before slipped away from everyday sighting to small miracles here and there. The water mostly stayed but has receded a little over the thousands of years.
The world was renamed Ark Terrash. The ensuing millenia saw many territorial and religious wars come and go between all the races. With many races leaving to form their own sects within the world on whatever land still peaked above the water.
Magic was effectively null for many centuries while the world recovered only minimal power was still active. As the world and gods slowly gained their energy back magic returned to all races, although not as prevalent as before. Even the humans were granted magical powers to keep the past from repeating itself. The stories are still told throughout the lands although everyone has a little different telling of it. The only constants are the Red Cloaks, Hallister, the gods and the bloodiness of the war.