"with few exceptions" I can't back it up with facts but I do have the impression this sort of thing is significantly more common in the US than in any European

"with few exceptions" I can't back it up with facts but I do have the impression this sort of thing is significantly more common in the US than in any European, Asian, African or South American country. I guess you would have to compile statistics for "Mass murderers with no clear motive per capita" and compile all the incidents going back at least 20 years and you might have evidence for or against. For example, I can imagine this happening in any African countries I am familiar with, so to me it is clear that there is an element of culture involved.