I've lived in the US for 10 years, and I follow plenty of world news. It is clear that Columbine-like shootings are (with few exceptions) an American phenomenon. [1]
Um, what? I can cite two mass murder incident in Japan off the top of my head. There is the Osaka school massacre and the Akihabara massacre.
I can think of several in Europe as well. Germany alone has suffered two double-digit-victim school shootings in the past decade, despite having a population 1/4 that of the US: http://en.wikipedia.org/wiki/Winnenden_school_shooting , http://en.wikipedia.org/wiki/Erfurt_massacre. It's interesting that the German media, at the time of Winnenden, often asked an analogous question to the one being asked here: whether it was becoming a particularly German phenomenon. Population-adjusted, it would be as if the US had had eight mass school shootings since Columbine, which it hadn't had.
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.
Um, what? I can cite two mass murder incident in Japan off the top of my head. There is the Osaka school massacre and the Akihabara massacre.