Group identity is formed in combination with group leaders and followers and assuming the group successfully functions (in other words, there is no insurrection by followers), the group reinforces its identity with hazing, intimidation or rituals. All groups of people are essentially "gangs". Some gangs just happen to be more violent than others. Even the "peaceful gangs" have group identity reinforcement mechanisms. Gangs could be based on race, political affiliation, geography, religion, etc.