The militias have been explained as a continuation of what were referred to as the 'death squads' in the 1960s, 1970s and 1980s, which first emerged in the west zone of Rio de Janeiro. These squads came about as a result of a lack of effective state security policies in favelas, coupled with widespread fear caused by unsafe and at times hostile living conditions.

Militias have gained the most territory in recent years, having obtained rule of previously neutral territories. they are thought to have gained such considerable power and scope because of their capacity to organize, as well as their use of violence.