I wrote earlier that I was trying to think of examples in history of mass movements of refugees/ immigrants. Found many references, part of one:
"In the 19C millions of people, including entire communities, from Ireland, Britain, Germany, Scandinavia transplanted themselves to the wide open spaces of the New World" - very few wide open spaces now.
"What happened as a result was a warning from history. immigrants came into conflict with the indigenous populations - Native Americans, Aztecs and Incas in the Americas, Aborigines in Australia, Maoris in NZ, Zulus and other tribes in SA. Leading to epidemics race wars and genocide."
There was an influx of Jews from Russia at the turn of the century and they had trouble settling. Later from India and Pakistan, similar problems.
This might be too alarmist, and no doubt some others on here will say I lack compassion, but if nothing else, a distinction should be made between true refugees from war like the Syrians, people from EU states, and others.