Don't think they're exactly no-go, but they're hostile to the police, and have become a lot more hostile thanks to Obama's demagoguery and lies. Europe didn't have them though until mass migration. So the causes are different but the result is the same, ethnic-cultural enclaves hostile to the society at large.
How did Obama make them more hostile? I keep reading that as if cops and minorities were cool with each other before. High profile events and everything being recorded probably are more impactful.