> various European nations [...] some immigrant groups
American Jew here, who spent years living in France and Spain. I've heard the same polite euphemisms refering to Arabs and Gypsies from the mouths of members of the Front National. You know, before 1945 it was said in Europe that Jews weren't able to integrate fully with the host society.
One might ask: Was that the Jews' fault? Or the host society's fault?
It's a relevant question. You are blaming it on the particular group of migrants involved in the case of Europe right now. But historically Europe has ghettoized other groups.
When the US ghettoized Chinese economic migrants, American politicians claimed they could never integrate. And yet the Chinese-American population is well integrated and hugely successful since the host society allowed it. Same with Jews in America, and increasingly with Hispanics.
Why is it that economic migrants do, after a few generations, become successfully integrated in America, while they tend not to in Europe?
I don't think the evidence definitively supports the conclusion that it's down to which group. Europe has a problem with integration that has its roots in the ethnic character of its states (something America does not have), in deep-seated xenophobia that causes social exclusion of immigrant or out-groups, and in the fact that its states' reasons for existence are based on tribal boundaries and wars for territory rather than on achieving broader democratic and economic flourishing by harnessing the capability of the whole population. And thus Europe presents neither a dream of integration nor a path toward integration (as in, "to become American"; there is neither an equivalent aspiration nor option "to become French"). And then, once again, Europe blames the groups it refuses to accept.