All of them had guns.
Hmm.
I'm not sure this is "clear" at all. Furthermore, what can you do about this situation? Should we make divorce illegal again?
Humans evolved in the most brutal of environments. Earth is literally a closed system, there is really very little material input from outside anymore. One way to thrive in such a system is to evolve aggression and a propensity to sudden violence so that you can eat other animals without feeling too bad about it. We are exceptionally violent, we came to dominate the globe because we are willing to do whatever it takes to survive. We cannot just 'switch' those tendencies off, they served us very well for most of our early history. I suspect our future is going to be determined by how well we can suppress or channel that tendency.
Young men worldwide seem to want to gain 'infamy/notoriety/fame'. Look at the vast majority of performing artists and DJ's and whatever. Many are male. There is a desire to stand out, to create something, to be credited with doing something. To be the author of ones fate in what appears to be a deterministic universe. In a vast globe of 7 billion, how can one make a mark? I'm of the view that creativity is the vital key to chanelling some of these tendencies away from destruction and into something useful.
I've often wondered if this sort of stuff happened in early human societies. Did young men suddenly storm into tribal camps with spears and start randomly killing people?