All right, so I'm thinking of dropping my faction on the northern peninsula by the Cursed Sea, as shown on this map:
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[img]http://i.imgur.com/B13Y2UN.png[/img]
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They are a nomadic, horse-riding people originally from somewhere north of the Justinian Empire, who recently began migrating south due to longer and harsher winters in the north. They fear the Great Cold, a prophesied eternal winter that will end all life.
I figure they walked across the frozen straits from the north-west during the height of winter and began demanding tribute from or driving out whoever lived there already. Perhaps a mixture of petty kingdoms, city-states, and tribes.

Aside from that, I've got a question pertaining to the map: I'm assuming Nagath is the area east of the Justinian Empire, is that right? You say the world is big, but do you have any rough estimate of how big?

Edit: I guess I should specify that we're human, since there seems to be plenty of people who aren't.