re: The streets of Paris now look like the slums of Nairobi

Likely in the 10th, 11th or 12th...and while not in the tourist areas, you can hardly consider it "not the main part" of Paris.

There's a lot of residents there and they all know how to burn tires and torch cars.

But to the OP. They initially needed laborers to prop-up their Ponzi scheme social net, but apparently didn't consider what would happen to their demographics and culture after 30+ years of unfettered "immigration".