Something has changed
Let me start by saying that I was born and raised in the US. Also let me say that I'm not opposed to gun control - I don't own a gun, and have never shot a gun (go figure, I'm almost 50). Also, I don't understand how over-the-top some people get about the idea of gun control (drinking the NRA cool-aid, so to speak...?)
At any rate - since colonial times, guns have always been accessible in the US. And so - the availablity of guns hasn't changed, and can't be the issue, therefore. The lethality of guns has changed - which is an important point - but still, school shootings are a somewhat modern thing.
So I have to ask, what's changed? I don't believe it's video games, or movies - I mean, we all played shoot-em-ups as kids - whether it was a video game, a movie, or just pretend (out in the back yard with our friends).
So something has changed. But I dont' know what it is...blah, blah, blah... (That is to say, I don't have an answer.)