Why do some children bully others?

Teenages aren't the only bullies. Bullies are everywhere, at school, the workplace and sometimes even at home. I suffered with severe bulying in my old school and it led me into self hate and a lot of trauma. People bully because of a lot of different reasons sometimes the bully could have been bullied to start with, or they crave attention from others or even they dont like themselves therefore put others down to make themselves feel better. Hope this helps