Interpersonal violence and confidence in yourself go hand in hand at the societal level.

Places where interpersonal violence abounds has people being so arrogant and believing in themselves that they have no qualms attacking others, because they KNOW that they can't possibly lose. This is Africa

Places where interpersonal violence is low has people being very conservative and avoiding confrontations because they are scared of losing or succumbing to them: this is clearly Asia and Europe to a certain degree

The US is in a sweet spot, actually it was in a sweet spot in the 80s, now it has abandoned it and moving towards European type society. Still it's the closest place to a sweet spot it once occupied and still benefiting from the time it spent in that sweet spot