Societies are complex, and humans are still very tribal. Any large influx of new population changes everything significantly, for good and for worse. And there will be resistance to change. Intermixing of cultures takes multiple generations, if at all and even then you will see silos.
We just need to look at how things are even now, even with the supposedly local population - caucasians, hispanics, african-americans and native americans. And they've all been together for centuries.
Societies are complex, and humans are still very tribal. Any large influx of new population changes everything significantly, for good and for worse. And there will be resistance to change. Intermixing of cultures takes multiple generations, if at all and even then you will see silos.
We just need to look at how things are even now, even with the supposedly local population - caucasians, hispanics, african-americans and native americans. And they've all been together for centuries.