Traditionally, it depends upon who lived upon the land and how long and under what circumstances.
The son of a gypsy is a gypsy. Even worse because they would act as one.
So yes, Id say that for most of history foreigners were looked down at, and the assimilation of people was seen as something you impose on people because you fail tor respect them.
The taking of culture within your own is something you do to make their own idea meld into yours, not vice versa. Historically this is crap like Regicide, or the Greeks doing to half the middle eastern world, or even. id say, the muslim spain or the unification of france.
trade relations and other such bitties are likely to spread culture but its more of a passive assimilation into your own rather than you spreading it. Cultures have to be fairly alike to be willing to exchange idea much, and third-hand culture does very poorly. How much chinese culture came with noodles to Italy, for example? What about how well the Europeans did in china?
Ties that bind often help, though Id hesitate to use irl examples. Lemme see ... nope, I can think of no non-modern examples of disparate cultures working together and spreading to one another.
Modern western ideas about and 'prosperity from diversity' and 'the moral goodness of acceptance' seem to come from an amusing mix of Christianity and enlightenment. The very scientific method, after all, is about diversity of idea.
P:
^^^ It is in the note, that cultures seem to spread over the axis of time better than distance. Orthodox Catholicism fed into the early enlightenment thinkers and created the scientific process we still rely on today. And the early thinkers did a lot of work with morality, which is kind of one of Catholicism's big claims, that it has spread meekness and acceptance for other cultures (that believe in Jesus as the Savior).
One brick at a time.