Men are not native to the “Known World” (or main continent) of Kythar. After landing in the northwestern edge of the continent, they proceeded to slowly occupy and conquer the remainder of it, bit by bit. Under the tide of humanity, the other races were often ruthlessly repressed. A lucky few were able to provide services the human nations found useful, and were allowed to keep a limited (and carefully controlled) amount of freedom. The not so lucky were forced into slavery, performing whatever duties their human masters required of them.
After occupying almost all the Known World, the squabbling human kingdoms (known collectively as the Twenty Nations) eventually came to live in a peaceful coexistence within The Great Dominion. While each kingdom retained a bit of individuality, the Dominion brought an end to their wars amongst each other, and organized trade and law throughout the known world.
Unfortunately, a massive slave rebellion led to The Collapse, the end of the Dominion. Following the Collapse, the individual kingdoms of the Dominion once again took up their fighting against one another, and many did not survive the years that followed.
Members of other races distrust, fear, and, in most cases, despise humans, for the most part. Those allowed to remain “independent” under the Dominion often continue their trade with the human kingdoms, but only as it continues to benefit them.