There's an interesting piece in Partisan Review on the gap between Islamic and non-Islamic populations in Europe

For all the racial and ethnic hatreds that fill the pages of American history, Americans, even bigoted Americans, tend to be better at this than northern Europeans are; we are accustomed to the idea that a person from anywhere can become an American. This is, to be sure, not a virtue on our part, but simply an idea we are used to. For many northern Europeans, it is not: it just doesn’t come naturally. More than half a century after the fall of Nazi Germany, the notion of ethnic purity still lives, unarticulated, often even unconscious, in the minds of people who think of themselves as good Social Democrats. For almost all northern Europeans, national identity continues to be wrapped up in, and equated with, ethnic background.

For this reason, large-scale immigration–of the right kind–could be a very positive thing for northern Europe. Certainly there are some immigrants from Muslim countries, people who have nothing of the fundamentalist about them, who have proven to be excellent entrepreneurs and model individualists in a part of the world where individualism has been traditionally discouraged. (Why? Because it’s viewed as a threat to social democracy.)

As an Australian, my first reaction to the mixing of ethnicity and nationality in Europe was one of puzzlement. The concept of nationality is a different one. It is possible for an outsider to become an American or an Australian in a way it isn't possible for an outsider to become a Norwegian. Europeans are puzzled by my puzzlement.