Thank you both, some interesting things to work from there.
I haven't answered because, to be honest, I haven't given ancient Kulthean planetary history much thought. I haven't even completely resolved (that I recall) rationalizing Althan/human common ancestry (clearly they have one, though both claim to be native to their worlds, not to mention all the other common species). Lots of Portals long ago.
I always thought that humans had been dragged to Kulthea by the spacefaring Althans (K'ta'viir) long ago, or like you said: a portal, but I do have another idea on that:
Humans didn't arrive on Kulthea until late in the Second Era when the Taranians crashed landed in their colony craft. (I would have the "Taranians" be a human sub-culture from Earth, or possibly a religious group fleeing persecution.) They did what they did in the official history, tried to stay hidden away from the existing cultures, but were dragged out of hiding by the Wars of Dominion. Their incredible technology would just be considered mighty magics by the locals and would have helped a lot against the forces of Unlife and the Dark Gods. Afterwards, staying away from the rest of the world was not an option, and they lost much of their technological base during the war, so they pretty-much had to join the rest of the peoples of Kulthea.
This means that the Second Era of Ire was dominated by Elves, they were the preeminent species of Kulthea, like the Althans/K'ta'viir were in the First Era. Now, with the decline of Elves due to the war, humans have become the dominant species during the current era, the Third Era.
Yes, this means that the various kingdoms of the world were originally elven nations, so the crowns, rods and swords of the Jamian kingdoms are connected to the original elven ruling families, which means that the current human rulers (who can attune the items) all have elven (royal) blood - which makes the current anti-elven attitudes of Rhakhaan somewhat funny.
Also, I think that 6,000 years of history during the Third Era is more than enough to understand why and how humans have spread so far across the face of the planet - especially since they started with a higher level of technology than we humans on Earth did, and they had help. (Elves.)
Whatcha think? (As it pertains to ancient history, I will put something together and post it, and you guys can tell me what you think about it.)