You'll probably get a few posts from me because after reading through pages and pages, you think about things and then forget.
Just quickly, someone said Kilrah's tectonic instability caused them to be aggressive. Well, you could think like that but how would that explain an aggressive race that lived on a very favourable world.
An example comes to mind, humans!
Its interesting to think that there is this forest that is split down the middle by the Congo River. On one side there is a group of apes that are peaceful and live together cooperatively. On the other there are chimps who violently attack one another. I wonder which side we're related more closely to...
Second thought:
Anyone remember the Bulrathi from Master of Orion. Big bunch of bear like creatures that would kick arse in hand to hand combat?