Why do people feel the need to get into a physical fight over small things?

Especially nowadays, kids in my little sister's middle school and the high school that my friend goes to there is probably a fight every week. Once or twice a week, I'll look on Instagram or Snapchat and see "Let me know if you have the fight video". One time, I was talking to a former co-worker and a guy who was a friend of mine while he worked there. I jokingly told him that he was bad at a sport and he said "Fight after work I'm dead serious" I told him I don't fight because it seems pretty dumb like what do I gain from doing it. Also, that is all I hear about everyone, I'll beat so and so up, I'll get them when they're not expecting it. Like who cares, just be peaceful and the majority of the time the things people fight about are small inconveniences in life. Can someone explain to me the reason? If someone is from a country other than the U. S. Is this just an American thing?
Why do people feel the need to get into a physical fight over small things?
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