Well, your lizardfolk revolted from the naga, but there are several tribes. So there has to be a reason why the unified revolt broke apart into several tribes. That's an ancient story that could be told.

And going from some other creatures on the barbaripedia:
- Bronze dragons allied with Elven clans. Seems like a great story: dragons living in the water allied Elves living in forests near the water. Why did they ally? Did they have a common enemy or something like that?
- Sahuagin, the fish people. Where did they come from? Why do they have a king ruling them when most other races are splintered and ruled by barbarian warlords?
- Trolls/ogres: The barbaripedia says they roam the lands trying to eat the other races. It seems to me that when the first trolls came to the barbarian lands and started eating people, that gave quite a shock.
When did that happen? What effect did it have? Was it an invasion or a migration?