1. Increased use of pharmaecuticals?
2. Increased exposure to violence on TV?
3. Increased exposure to violence in video games?
4. Unknown/unrecognized societal factors and pressures?
1. Americans prescribe more medicine for mental conditions than any other country, PER CAPITA (meaning not just the number period, because we have a huge population, but the number per person) and some of the LOWEST per capita pyschologist/psychiatrist therapy sessions. Basically, we are replacing drugs with human interaction.
2. and 3. We have pretty much the same TV programs as most other countries, but they don't have an issue like we do. The same is even more prevalent with video games. There are some really REALLY messed up video game mods (someone taking a pre-existing game and changing the story, characters, etc) that are coming from Europe and especially Japan. So that's not necessarily what the problem is either.
4. BINGO. America is a unique "melting pot" of cultures, and in this case, causes of violent behavior. It's not ONE thing causing it. It's a lot of things, but the biggest is that 99% of these shootings are from people who are screaming for attention, and aren't getting it from their friends and family. So they look up and see us holding these people like Adam Lanza up on a pedestal, all over the news, getting MASSIVE amounts of attention, for what? For shooting people, innocent people. So now these kids see this and think in their messed up, jacked up head of theirs "Hey, thats how I get attention." Next thing you know, a school, a mall, an office building, whatever the place, it's being shot up.
I don't know if you have ever heard of the guy, but Mr. Colion Noir does a good video summing up this subject.
WARNING: There is one little "bad word" in there.