America is a violent nation, of which such violence is especially lethal, because of the high prevalence of weapons such as guns, which are quite potent in their killing effectiveness. Because so many Americans have fairly easy access to guns, this means that those having a quick temper or are prone to violence or to retribution or to intimidation or to revenge, have a ready weapon that can harm and kill other people in the blink of an eye.
So then, one of the main problems with why there is so much violence in America is the fact that Americans have a preponderance of weapons that are violent in their effect upon humans, and the person utilizing that violent weapon has made a decision, thoughtless or not, of which the result has a very lasting effect. So too, America in many ways, is a country in which so many of those that feel that they have been disrespected or have had their personal space or personal territory violated, will react in a manner in which to retrieve that respect or honor, they will strike violently at the person that has violated them.
It then can be said, that the sheer quantity of these instruments of violence in the hands of so many that have not the maturity to look at other alternatives before the use of them, is one of the most salient reasons of why there is so much violence. Additionally, it doesn't help that so many believe that the use of guns is an appropriate response to having been violated, or disrespected, or having their honor impugned, in which one of the reasons why firearms are preferred is the person using it, recognizes that the physical distance between them and the person that they are shooting at, is great enough, that the person with the firearm is realistically in little danger of harm from the other, and therefore can extract "fair" retribution without any real risk of retaliation, at least, at that particular moment.
The fact that America has been so violent for so long, would further indicate that America has done a poor job in addressing the construct of how to appropriately respond to being dishonored or humiliated; for, quite obviously it is seldom appropriate to kill somebody, in response. What has occurred, regrettably, is that much more violence is prevalent in lower socio-economic areas, probably because those people have already lost hope as well as their good dignity, and are therefore more prone to respond to being insulted in a manner that involves some violence, simply because of their joint feeling of hopelessness and despair.
Those that live within conditions in which they are ill educated, and are from dysfunctional families, in which fair opportunity and a pathway to mainstream success is basically precluded to them -- will often feel humiliated in their person, for their lack of success. This, thus means, that these people are going to be ready to fight at provocations that a more mature, a more reasoned, and a more successful person, might well brush off; and thereby do often strike back at those that have offended them, in the belief that the respect that they do desperately desire, will come only from the destructive bullets shot at another from their gun.