You people are the loremasters, and this isn't the Oblivion forum. Don't say that there's no lore when there quite clearly is. The difference between Morrowind and Oblivion is that Morrowind told you things; in Oblivion you must find them out for yourself.
If you come to your own conclusions, you will find out a lot about them. The settlement of Border Watch has a Khajiit tribal leader, and the houses don't look like they were occupied without fighting. There are considerable amounts of skooma in Leyawiin and Bravil, which is referenced by in-game speech:
"The skooma trade is making a lot of money for the tribes in Elsweyr, and a lot of that is going to the Renrijra Krin."
"Sounds like the Empire has given up on stopping the skooma trade in Elsweyr, and I hear tribal chiefs are supporting the Renrijra Krin."
It does not appear to be the Renrijra Krin that are selling the skooma, they simply profit from it. It seems that local groups of criminals, such as those in Greyland, sell it and give the Renrijra Krin most of the profit.
"We need some law-and-order... bring in the Legions. 'Leyawiin for the Imperials,' I say. No sense coddling those Renrijra Krin bandits."
There is a mercenary, S'razirr, in the game who is in the Renrijra Krin, and he is noted for having a lot of arrows in combat. He also can be bribed, and as he is a mercenary it seems that the Renrijra Krin don't just rely on skooma for their income. They have also left Leyawiin with few political allies - the people claim that the count says that it has to do things for itself when you close the nearby Oblivion gate.