I think everyone knows that aggression is not innate. This behavior can be shaped by the environment, family problems, and so on. The most common causes are low self-esteem, childhood trauma, family problems, exposure to violent behavior. You can learn about [bulluing behaviour](https://www.australiacounselling.com.au/what-is-bullying-behaviour/) here . The article also details the consequences of bullying. The abuser, like the victim, also needs psychological therapy.