What is causing all the recent school shootings?

in the past years there have been 47 school shootings since Jan 1996, 43 of those have been in the last ten years. in the last five years there has been 15 school shootings, 5 of those happened last year. this year we have had 2. What is causing this out break of violence? is it the fault of the Parents? the Teachers? the Peers of the Shooter? is it caused by stress that is the fault of the School? the Government? what is the underlying cause of these Stand-Alone Complexes?