Well... the sicilian mafia comes to mind... the french can be quite violent too... Western Europe is not so bad either, with guns.
I guess you mean "normal" non-criminal people in the EU are not allowed to have AR-15 assault rifles in their homes, that they can use if they have mental health issues.
I personally believe that is one of the reasons the USA has so much gun violence. Get rid of the guns in people's homes and things will change for the better.
I mean ... look at this ... Only in the USA!
https://dimages2.corriereobjects.it/files/image_572_429/uplo...