How does that happen? Why is it happening with more frequency in recent history? And most importantly, how the fuck do we stop it?
Wikipedia has a list of rampage killings dating back to the mid-1800s that's pretty damn long, so these kinds of things have probably been going on forever. And while they aren't unique to the United States, we sure do have a lot of them. Nearly all spree killers are male too. I'm not sure what that says about the male brain, and more specifically the American male brain, but it probably says something. Is it less empathic? Does it have a greater propensity for violence? Is it more prone to severe mental illness? Is it more likely to lose touch with reality when stressed? I don't really think being male is a significant piece of the puzzle, but it may be a piece, whether biological, cultural or both.
We can point to the usual supects too, of couse: guns, video games, movies... but those are not causes. If they were, we'd be witness to horrific rampages in every neighborhood on a regular basis. But we're not because spree killers are a uniquely defective breed. I think the only true solution to their kind of madness is to learn how to identify it early and either treat the abnormailty successfully or remove them from society and keep them locked in padded rooms.