Social evolution is as dynamic as biological evolution. Many believe, however, that their own migration or that of their forebears was the last one, marking the end of history. The occupied territory then becomes an endowed part of the self. Meanwhile, however, human migration continues. Other folks are on the move, pressing into the same territory, first into the country, then into the neighborhood.
Perceptions differ, of course.
One's own migration is the search for a destiny, the quest for the promised land, but the other's migration is an incursion, a threat, an act of war. The treatment of outsiders has ranged from disdain and discrimination to enslavement and genocide. While the United States was expanding, this aggression was not only directed at incoming migrations but also at conquered populations. Today, the aggressive themes focus again onimmigration. The influx from Europe continues, albeit at a slower pace and from different countries.