Young men in other countries play the same video games and watch the same movies and do not commit as many mass killings as American young men.
They probably just don’t want to.
But we've had crazy people forever. We've had semi-auto weapons and high capacity magazines for over a century. Why is it then that this trend has now started and is accelerating? I believe that the violent visual media play a large part, especially when they come to serve as an alternative reality for the socially maladjusted and withdrawn schizoid personality types, as seems to be the common thread in too many of these cases.
And yes, these are available to youth in other countries, but I remain unconvinced that they are as saturated in it as are American youth. Perhaps someone can show me some studies to prove me wrong, but it seems to me that the pathology is proportionate to the time spent in these media.