According to mythology the hero Davidion, king of the area of the Great Lake, who fought in the siege of Dorstulon, the city of the ten walls, famous for killing the king Lerimeus of Zophron, had 4 sons: Ikarus, Lodaimos, Kushi and Arsi, each one of them formed his own tribe, in the region previously ruled by his father. After a terrible drought they have to flee, Ikarus fled south and became the ancestor of the Ikarians (and by extension of the Blatians) and the Oronai. Lodaimos travelled also south and became the ancestor of the Kallian peoples. His brother Arsi went north, and his tribe became the Crorai people, and finally Kushi crossed the Suris Straight and became the ancestor of the Seris people.
Historians of our age can't really say if the myth is true or not, although it may have some historical accuracy. What we do know its that all this nations share a common pantheon on gods (but with different names in each one of those realms), that their languages also have a common ancestry and speakers of these languages can sometimes, not always, understand each other because of the similarity of words and grammar. Some customs may have a common origin, for example we know that all davidovian peoples use bronce objects in their sacrifices as they consider it to be a sacred material reserve only for performing this kind of rituals or the fact that they all make libations to their gods, as it appears that this wasn't a custom of the indigenous peoples of the areas they settle in.
It is believed that the first humans that populated the region of the Kallian plains since around 6000 BP were conquered and assimilated around 2400 BP by the Kallian people, from whose language only a few words and sentences survived, but they are clearly from the davidovian family of languages. The ancestors of the Ikarians and Oronai settled in the area behind the Great Mountains and the west of the Peninsula of Morya, to the north , the Cronai settle in the area close to the Nords while the Seris crossed the straight of Suris and established their realm on the other side, becoming, until the establishment of the Republic of Valia, to be the easternmost of the Davidovian peoples.