The cultural change often causes lot of social conflicts. It can happen quickly or gradually. It can be because of mass movement of people, or because of change of perception.
Which ever way the cultural change takes place, it always has its supporters and critics. Because the culture is something that is deep inside every person, pretty much the identity of that person, a change is very often not seen fondly, and more as an act of invasion. That has almost always led to big conflicts, and unfortunately lot of lives have been lost through such conflicts.
immigrants from northern and western europe continued coming as they had for three centuries, but in decreasing numbers