I can to disagree. In my state in particular, we had our first contact with Italian and Turkish guest workers in mining in 1960. Almost all men were employed in mining at the time. The foreigners have settled in our communities. There were many contacts and friendships between the nations. But there was also isolation among foreigners. This was not because of the Germans. My parents-in-law also came as guest workers and did not want to have any contact with the Germans. They lived with their compatriots. But it was that it wasn't a problem - it was good. Everyone else has blended into our lives, as in metropolitan areas as everywhere. There was a fundamental difference. Miners are all friends and kind of brothers. The integration came through the workplace. In 2015 everything was completely different. We were put under pressure with the wave of refugees. At first we were told that we have no skilled workers, which was not true. Then Merkel kept saying that we have to recruit the skilled workers from outside. Suddenly the strangers came and were introduced to us as our skilled workers. You noticed immediately that is was not right. Our Turkish friends also said that these are other Muslims. It was a culture shock for us. Then we should adapt and change under duress. This was never the case with Turks and Italians. We have been very happy to accept your culture to this day.
Nachtweide, when you hinted at the time before 2015 I didn't know you were actually thinking of the 1960s so we were probably talking past each other. Since this is the Corona thread I'll be very brief.
My understanding is that the much touted integration must have gone wrong at some point in time, probably as early as the 1980s, the time when Palestinians were fleeing to Germany because the Israeli military were killing the people at Sabra and Shatila (Lebanon) and German authorities started accepting anybody from the Muslim Brotherhood to the Grey Wolves (Bozkurtlar).
I have certain doubts about the integration of many Turks in Germany when President Erdogan, on one of his unavoidable electioneering trips to this country can rally hundreds of thousands of followers ecstatically waving their red flags, or women hardly knowing the language because they are quarantined at home by their culture.
Of course everybody knows quite a number of Turks that have integrated very well and so do I.
So Middle Eastern parallel societies may just be a problem of major cities and industrial areas and hopefully not where you live...
(Just my two cents. I'm sorry for the noise)