Instapundit put up this link from The American Interest EU Projects 3 million refugees and migrants in2016. Some comparison is made to the peak years of mostly European immigration to America, 1880-1924. We responded to that by dramatically reducing immigration at that point, but I think there was another connection that is not often made. It is also why we had Prohibition. There was a dual idea that we had to make sure all these foreigners learned how to behave properly, and we feared what they would do drunk. Also, there is usually a sentiment in all societies that if the good people are really, really good, God will bless the whole nation. So we got swept into a crazy whirlwind of an idea that a majority opposed.
There might thus be other odd things that happen if Europe keeps receiving such large numbers of folks very different from their current selves.