It's very hard for a newcomer to Charted Space to 'get' the Vilani presently, and I very much intend to go about changing that.
That's encouraging, I hope you do. It's a glaring problem when the overwhelming majority of the Imperial population isn't really characterized.
There were probably trillions of Vilani living in the Ziru Sirka at the time of the Solomani Conquest, so if every Solomani married a Vilani spouse, all that would happen is that the Solomani would be assimilated into the greater Vilani population like a drop in a bucket. This assimilation would only happen on worlds where Solomani visited or had families. A small military governance team or even a military garrison would make no difference. There would still be at the very least hundreds of billions of pure Vilani, ethnically, culturally, and linguistically. Over time, the Vilani language might pick up some loanwords from various Terran languages and Rule of Man Anglic, maybe some fashions, music, and perhaps a few customs.
But then the Long Night cut off all contact with Terra and the Solomani Rim for 1500 years. Vilani ways would predominate, and in time Solomani customs and language would disappear. Only on worlds with a large self-sustaining Solomani population would anything Solomani remain. During the Long Night, interstellar travel was at a bare minimum, so there weren't great flows of people between worlds. I'd say there probably weren't any, with all the reavers and pirates that canon assures us were ravaging the spacelanes. Therefore, worlds with no or few Solomani would be Vilani through and through. On worlds with large Solomani populations, like at least 100,000, there would be some mixed people, a remaining Solomani community, and the vast majority of people would be pure Vilani. On worlds that had large evenly-sized communities of Solomani and Vilani, there would be a pure Solomani population, a population of mixed people, and a pure Vilani population.
There's this old idea that when two groups of people inhabit the same area (like a continent or a planet) they all inevitably become intermixed, like pouring two flavors of soda into a glass or something. But that's not what happens. It's more like a Venn diagram. Exceptions are times of conquest. The men of the defeated population are killed, and the women end up with men of the conquering population, willingly or not. This is what creates somewhat of a total mixing effect. Even then, there will still be pure people of the conqueror population, since they will have families from the old country that will join them. Another scenario is when one population is devastated to the point where its members have a hard time finding marriage partners in the areas where they live, so they take up with whatever they can get of the choices available.
Another important factor is cultural perceptions the populations have of each other.
Vilani would probably consider Solomani absolutely disgusting. Most Solomani the Vilani would've met would've been spacefarers and military personnel who brought plague after plague, including the plague of STD's. There probably would've been immense social pressure on Vilani women to have nothing to do with these dirty destructive invaders. The Solomani ruined everything. They brought war, plagues, and in their foolishness they swept away the social, political, and economic foundations of the ancient Ziru Sirka. Their Ramshackle Empire lasted only a few centuries, and then everything descended into darkness. But, I suppose some Vilani girls will do anything for a credit, so intermixing occurred.
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