and the Sixth House are still at large, what would happen? We know the snow demons invaded back in the 2nd era and it looks like they both had a interest in conquering Morrowind and red mountain too since the demon king Ada Soom fought with Almalexia and the Underking in the battle of Red Mountain. If they had invaded around the same time as Morrowind right when the Nerevarine got off the boat, what would had happen? Terrifying snow demons meets bizzare cult mutants and ash creatures. Would they ally with the Sixth House or would they tried to fight with them as well?
Both sides required Divine support from the Tribunal
Vivec needed to flood the entire land while Almalexia needed the help of the Underking to defeat the powerful demon king Ada Soom in Red Mountain back in the 2nd era.
The Tribunals are forced to create a large mighty magical fence to surround Red Mountain and prevent Dagoth Ur and his legions of Monsters from expanding. Dagoth Ur and his Ash Vampires also managed to drove Sotha Sil and Almalexia away.