Kobolds arrived on Oceana in 300 BCE. They initially landed in the southern part of the temperate zone, just north of the wine & olive band.
The Kobolds first war was with the Dwarves. As they lost ground, some clans scattered to other islands. This was particularly effective in getting away since Dwarves were not a seagoing race.
The Kobolds next war was with the Roman Empire. This was only a few clans of Kobolds and didn't involve all the Kobold clans.
Over the next millenium, Kobolds, and many other races expanded to the west. As humans expanded, the Kobolds mostly moved further west. There were still some clans of Kobolds living in the eastern part of the world, but their size is small, and they have settled into a client status with the humans.