After more than a century in what is now Sanzoriland some tribes moved west into unexplored mainland. The Vasitorin Republic is a conglomeration of tribes which formed a single nation in the face of a war with another group of tribes.
These tribes spread out and flourished in their new land. However, they began to have contact with tribes spreading south from what is now Dominon State of Yimmen. With tribes having settled on Koneg speaking many languages, their time apart made communication even more difficult, resulting in skirmishes between the tribes. eventually, this escalated to all-out war, where the tribes which came from the north banded together to form a union and fend off the attacking tribes with a unified front.
After the war, with many of the tribes being severely weakened, one tribe took the opportunity to seize power over the others, with whom they had just fought beside. While there are still very clear signs of the distinct cultures, the modern day Vasitorin Republic is largely homogenous and those born there identify as one culture.