>>215698207 (OP)
It will be worse than Brazil.
For all the problems it has, and despite its continental size and regional variations, Brazil is remarkably monocultural. We have no Muslims, no Indians, no actual Africans (they're pretty much all mixed, even more so than the whites), very few actual natives. Everyone speaks the same language and had the same religious upbringing.
Our three main groups are injuns, blacks and whites. Injuns and blacks had no civilized culture, they were jungle peoples before meeting whites, so they know no culture other than the one that the white man taught them. They have no sharia law, no halal meat, mosques, cousin marriage, no language other than Portuguese, no literature and religion other than Western literature and religion.
Lusitanian culture has actually assimilated those peoples. It took some time and a few conflicts here and there, but eventually it did so.
That same culture never managed to assimilate Muslims. Think about this.
In Europe, I think there will be actual civil wars in this century, at least in some of the countries.