I wrote earlier about the 2nd Amendment, which is part of our problem, but the other part is the gun culture. It isn't so much violence. Violence is a problem, but it's far from a particularly-American problem. What is particularly American is that our violence so often involves firearms. The best contrast with us is the British. This country evolved from English colonies, and the English have a fairly high level of crime; soccer-fan hooligans are a cliche. What they don't have is our level of shootings.
I give a lot of credit to Sir Robert Peel.
When Peel established the Metropolitan Police, "Scotland Yard," in London, it was basically the first modern police force. There were police before him, but they were essentially localized watchmen. Peel reinvented the concept. Crime was rampant in his time, and some of the criminals, highwaymen, were popular heros. At the time, gentlemen had firearms, and so did many criminals.
Peel decreed that his police -- the "bobbies" were named for him -- wouldn't have pistols. To this day, few British police are armed. (Or, rather, they are armed with night-sticks.) The other response to armed criminals that is in the model -- I don't know how universally it is practiced -- that a policeman is not supposed to back down from a pistol.
If you rob a store in Chicago and a cop comes around, you can escape if you get the drop on him. If you try to run, he'll shoot you down.
If you rob a store in London and a bobby comes around, you can escape if you can outrun him. If you point a pistol at him, he is supposed to keep coming after you. (And few enough bobbies are killed that the entire police force of the UK hunts for any cop-killer; everybody is certain that if you kill a bobby you will spend the rest of your life in prison.)
I read some time back an article written by one of the few British police who were trained in firearms. There was a report of a group which was planning something violent. Since they were reported to have guns, police authorities sent a squad of gun-carrying police to confront them. Instead of guns, the perps were armed with clubs and knives. So the police, who had guns in their pockets, met them with night-sticks. If you don't shoot, British police won't shoot you.
Okay, this might have no impact on Newtown. Chicago, though, lost more school kids to gun violence this year than Newtown did. They just didn't die in one single incident.