* Intolerance and segregation. The more separated people are by race, class, gender, etc. the more they tend to think of different as "other," lesser, and fair game for torment. The more integrated, the better the chance of making friends across the lines and learning to use diversity for constructive problem-solving.
* Violent propaganda. It is widely taught and demonstrated that "might makes right." This plays into a massive morass of violent problems in America today including child abuse, domestic battery, police brutality, etc.
* Poor job prospects. People who can't get a job that pays enough to live on feel frightened and angry. It is difficult or impossible for them to participate in society, so they feel little if any loyalty to it.
* Social fragmentation. When job options, home insecurity, and other forces drive people to move frequently then that shatters social ties. The family has gone from extended to nuclear to now having lots of singles and single parents. When people don't have a social support network, that undermines their ability to handle challenges well. It also means that more kids grow up without learning a good set of coping skills.
* Lack of meaning. People want their lives to matter. They want to make a difference -- usually, want to make the world a better place. Profession, relationships, and home are among the things most people turn to for meaning. Unemployment and menial labor, lack of family ties, and frequent moves undermine that sense of significance. People go looking for ways to fill the gap, and that can leave them vulnerable to cults, violence, and other problems.
So how do we fix it?
Gun control will help little if at all, because the problem isn't the guns. It's the people who think that violence is a good way to express feelings and solve problems. Even if you could take away the guns, they would just find some other way to make trouble, and some of those ways are MORE damaging. Like, say, bombing a family health clinic or burning down a church, two other problems that are spiking right now for largely similar reasons. Or maybe they'll join the police where their coworkers will cover their ass if they decide to shoot people.
Things that would help reduce the level of violence:
* Teach emotional first aid skills, both for yourself and for others. Right now the average EFA knowledge is so bad it's like not even knowing that scrapes need to be cleaned so they don't get infected and you shouldn't put butter on a burn. A great deal of harm is done by not treating small psychological injuries, or not noticing that someone is having problems, which means they get bigger. Know the warning signs for mental illness.
* Teach tolerance. Teach coping skills. These have some innate instincts but are mostly learned techniques. Anyone can grab a poster of coping skills, stress relief activities, conflict resolution, tolerance principles, etc. and hang that at work or school or wherever else someone will let you post it.
* Integrate and relate. Encourage people to mingle in different combinations. Make meaningful connections with others. Look for common ground. Know how to promote diversity. Mix It Up At Lunch was designed for school children, but can work in any large group.
* Discourage violence; don't repeat or promote sayings that condone it. Instead teach peacemaking skills, de-escalation, and nonviolent conflict resolution.
* Provide resources for self-regulation. These may include quiet rooms, reference materials, comfort objects, or whatever else helps people feel safe and calm after something upsetting. Quite a lot of violence -- especially in public places -- happens because someone gets wound up and then has no way to wind back down. That means the next thing that can go wrong tends to trigger an outburst, sometimes a violent one. Think of these as social firebreaks: they prevent small problems from becoming large problems.
* Establish a right to work. It's not that there's a shortage of workers or work that needs doing; what we have is a resource distribution problem where a few people are hogging so much wealth that it doesn't leave enough circulating to meet personal or public needs. Restore the high-tax-bracket system that was developed after the Great Depression, and that would fund public works and public-service jobs for everyone willing and able to work.
* Similarly cover the rest of people's survival needs. Nothing makes people feel threatened, panicky, and belligerent like not knowing if they'll be able to keep a roof over their heads and food on the table.
* Support meaningful work. If the only jobs available are trivial crap paying starvation wages, that is miserable. Bring back the good jobs; penalize companies from shipping them overseas. Promote co-op businesses.
* Always balance authority and responsibility. Authority without responsibility encourages people to mistreat those below them. Responsibility without authority saddles people with a job they can't do for lack of resources.
* Make sure public authorities are professional and accountable. Not only is this essential for proper function, it also cuts off a source of encouraging misbehavior through example. When the authorities behave abominably and get away with it -- when priests rape children, police murder civilians, soldiers bomb hospitals, politicians routinely lie, executives create products that kill people, etc. -- then other people may think, "All I need is more power and I can hurt people however I want." This is not okay. This is not how a sane society works. When public authorities are held accountable for misbehavior, both they and others will behave better -- or get replaced with someone else who will.