the problem is that these mayors did their very best to make these people feel as if they hadn't relocated to the west,
as if they could still live their own customs and stay amongst each other as if they still lived in their home countries
(except the benefits of Belgian social security)
it is quite the opposit of social exclusion
in the US this would not be possible because you can't live on welfare for generations
I don't know why you have that impression. It is indeed possible, although there are periodic attempts to institute work rules. If my memory serves, people on public assistance form a much bigger percentage of the population in the U.S. than in many countries in Europe.
We also have the situation where rioting is permitted to continue out of fear that police intervention will make things worse. The media run with questionable stories blaming white people or police of any ethnicity, stories which are later proven to be untrue in most if not all cases, but by then the stories have become "urban legend", and the media make no concerted effort to give the "true" story as much "play" time.
The difference is that the ghettos here are predominantly African-American or Hispanic, although I just read about an area in Michigan which is predominantly Somali which has incredible homicide rates because of Somali gang violence.
So, we have ghettos too, both "native" and created by recent immigrants. And yes, many of the problems of the people in those areas are in the nature of self-inflicted wounds. That doesn't mean that the surrounding, larger society is blameless. There is still racism in the U.S. even if it's much better than it used to be. Many, many African Americans and Hispanics have and are moving into the middle class even if they are still segregated to some degree, but there are still the members of the underclass who are unable to rise out of their situation, because of lack of opportunity and skills as well as other things.
In terms of immigrants, it's just incontrovertible, imo, that they are more accepted and more easily integrated in the U.S. than in Europe, particularly if they are not African immigrants. I'm being honest here. It's sad but true that a Middle Eastern immigrant has an easier time here than an African immigrant or African American native.
Yes, many recent immigrants tend to go live near compatriots. That was true for the Germans, Irish, Italians and Jews as well. By the second and third generation they seem to start moving "out", which was also true for the "white" immigrants. However, a Syrian immigrant, for example, doesn't have a hard time getting housing in a non-ghetto area and when they do so they are largely accepted by the surrounding community. Their children become Americanized and accepted pretty quickly. It's even more true for Christian Middle Easterners who are quickly accepted into Catholic churches, and helped by them as well.
For many reasons, it's just not as easy to integrate in Europe, and that's true not only for migrants from the Middle East and North Africa but for migrants from one European country to another. I'll leave it at that because I don't want to get personal about it.