I think the real question is what's unique about the United States. Events like these have become, sadly, almost commonplace here. There is obviously, like or not, something deeply wrong with the American psyche that isn't present in practically any other western, civilized society in the world. Is it that our media is all that different? Is it because we've departed more from 'family values' than European cultures have? Is it just because it's easier to get guns? Is it because we glorify violence and going out with a bang more than anyone else?
Or it's something else?
In American and now in British culture individuals are encouraged to succeed and strive for wealth.
The media encourages this ideal at every opportunity.
The majority of individuals are given a ideal which for the majority is unobtainable.
The inability of the of the individual to realise that mediocracy is the lot of the majority.
The result is mental instability and a violent out burst to this problem.
In education today the student is informed on a regular basis that his viewpoint and opinions are valued, this again causes problems when this falsehood is realised.
Mental issues are increasing in Western society due to this problem.