I had to enter into deliberations with Vilage on the matter of your app. I would Gorgen if he was on, since he has people related to his own people in the region (namely in the islands south of you, and I'm holding off making an official comment until he gives me a siren app). And since concerns of avoiding random bubbles have come to me, it's probably best to say something.

The biggest issue and hole is the claimed life-style your people have. It's been four-hundred years since the collapse of the Vishput so they would have been there for about that long at least. That's more than long enough for even the most nomadic of culture to mostly adopt a life-style adapted to that region. And in an area with a defined river and so coastal and lush chances are agriculture would have been picked up, whether on their own or adapted from the "exterminated" locals.

A comparison may be drawn from the Magyar or the semi-nomadic Arabs who in settling in or conquering their respective areas (to the Magyar Hungary and the Arabs everything else). Where there was a present agricultural complex for them to adopt or even cities pockets of their society would have adapted and grown from there. In the case of the Arabs it was them adapting parts of Greek culture and using the Byzantine administrative systems from which they built their cosmopolitan, urban culture. For the Magyar it was taking over the admittedly sparse farming homesteads in the Carpathian basin where Hungary would be born.

Point being, after four hundred years nomad-ism and a food source revolving around goat herding would have fallen by the way side or would be on the way to doing so. It's not to say that it would all but disappear, since even after a thousand or more years of having a urban society the Arab populations still have their nomad roots and the Bedouin - an Arab tribe - still freely practice a nomadic lifestyle despite the transition from semi-nomadism to urbanism in their more populous family tree.

And that region having Visha influence to and having been administrated by them from below there would have been some manner of organization to keep the local above-ground populations producing for them.