In this version, the Thri-kreen are the nomads while the Tohr-kreen are the city builders. There are references throughout the fluff posted above to the two groups, giving some insight into each. I'm trying not to go too much into them, as I'd like this to be something that can be easily added into games rather than becoming a campaign setting itself.
Edit: On another note, I've got both of the prestige classes posted. I'm pretty tired though, so I'll get the next section formatted and posted tomorrow.