The "no-go zones" trope is a disgusting, racist conspiracy theory created by American right-wing xenophobes, and exported to their anti-immigrant counterparts across the pond. It is a product of the era immediately following the attacks on September 11, 2001.

The main claim is that there are specific areas within European cities which have been "taken over" by immigrants, usually Muslims, which have become "unsafe" for white or non-Muslim citizens to exist in, especially after dark. The more extreme claims state that "islamic extremists" have replaced the existing order with "sharia law".

This is racist, Islamophobic, and false.

In reality, racists and xenophobes simply do not like immigrants (especially the brown kind who talk funny and pray the wrong way) forming their own solidarity networks, running their own schools, and getting involved in their own local governments. They especially do not like them making time and space for their own forms of worship in their own communities, and will often claim that forced conversion is occurring in these areas, and that schools and governments have been "islamized".