America is a 'melting pot', it used to be said - everyone adds their own stuff but it's part of the same dish.   In the 1970s, partly due to elitism and partly due to idealism, that began to change and multiculturalism took hold.  America was not a melting pot, proponents said, it was a salad bowl and each part needs to remain whole.  People who dislike foreigners happily embraced that progressive idealism.

No place took to multiculturalism more than Germany.  Some of its reasons were pragmatic, though vaguely racist - multiculturalism meant Germany could import workers to help sustain the aging population that could not be supported by lower German birth rates, but not letting them be citizens and encouraging them to live in their own parts of town was just modern ghetto-ization.
And it's failed, says Chancellor Angela Merkel.   30% of Germans now say the country is overrun with foreigners, and they truly mean people who have no interest in German life or culture but to whom it is just a geography.   Foreign workers are now in their third generation, and still they are not citizens and that population boom is a concern, says Merkel.   2.5 million Turks alone live there.

The solution, says Merkel, a conservative, is to require knowledge of the German language, to help people integrate - because Germany can't afford for them to leave but they now understand the risks of countries within countries.