For Rok - The simplest definition of a mass shooting is a gun crime in which at least four people other than the shooter are killed. Over the decades the number of these murders has zig-zagged up and down without a discernable pattern. There have not been over 100 of these this year so go back in your hole.
The rest of the world has them aswell, we have the best media coverage in the world, most complete I should say.
Most of the mass shootings have a common theme, either a history of mental distress and/or the use of psychotropic drugs by the offender. We corner the market as a society on these drugs. You could also say the breakdown of the family and traditional values but I dont really buy that. The narcissistic tendencies that get brought out from our instant fame/selfie/instant gratification/entitlement era we have now. Dunno, just some ideas.
