Okay here's the first history. The White Wanderer is the creator of the multiverse. He created many worlds, etc. He made Arinar and placed a spear called the Warspear. (it's said that it's the same material as miracle coins lmao) He entrusted three gods, Garaan, Harad and Nuadu. In secret Garaan wanted power and he allied with demons from another dimension to get the spear from Harad and Nuadu. But it wasn't enough because Harad and Nuada beat Garaan and they imprisoned him.
Years later I guess, Nuadu created the Elves and the Moon. Harad created the humans and the Sun. The king Orin found the prison of Garaan and he was transformed to become the first forsaken. The story has skipped and with the Forsaken and Mountain Clans, a great battle occured in the grove of the Warspear. And in the battle the Warspear was broken and the Sentinels won. The Humans that participated were called by Harad the Chosen.
In my understanding the origin of the mountain clans is that they were lead by Berengar and they were betrayed by their fellow humans amd they despise their fellow brethren and elves. (they werent called chosen before) When Garaan was wounded, his drop of blood created the lizardmen. Idk the origin of the merman and gnolls, etc. The Elves Capital Maliat was destroyed by the legion. The norlant kingdom was also destoyed by the legion. Then the surviving alliances retreated to 4 separated islands.
And that's all I know. People can add more facts if they want to.