It's purely a propaganda phenomenon. The actual violent crime rate across the US is at a 20 year low.
The leftist Mainstream Media in the US is determined to push the administration's gun grab agenda, so they make sure than any incident that can make people afraid, especially if it involves making them feel their children are in danger, gets top priority and incessant coverage. Just as stories that involve a citizen thwarting a crime or saving a life with a firearm are ignored across the board - those stories only appear in local news media, they never get national coverage.
The old newsroom saw is "
If It Bleeds, It Leads." Nothing gets eyes glued to the screen like fear and mayhem.
If you pay attention, you'll also notice that they use lots of calculated misrepresentation - every rifle is "
an AR-15 'style' Assault Rifle" (even though they never are), the statement that
"there are no background checks done for sales online and at gun shows" is constantly repeated, even though it is
absolutely false, the very term "Assault Rifle" is itself a lie - a true "assault rifle" is a fully automatic
machine gun, which are only available to licensed collectors after much paperwork and several background checks by the FBI. The guns currently targeted by hysterical politicians are standard semi-automatic (one squeeze, one fire) rifles with a military-looking grip, no more dangerous than any hunting rifle.
There is no 'phenomenon' going on. It seems that way because of the manner in which it's being covered by the Media Propaganda Machine. The truth is, if you want to see a chilling cause-and-effect link between violent behavior in young people in the USA, just delve into the correlation between bizarre homicidal outbursts in young people and the listed side effects of SSRI medications, like Ritalin, Paxil, Zoloft, Effexor, Prozac, et. al. But the MSM isn't going to cover the sins of Big Pharma, for fear of losing all that ad revenue they get advertising Viagra, Levitra, Abilify and Ambien.