The Evolution of gangs
Gangs develop because of a lack of psychological needs, says Abraham Maslow, these needs come in a hierarchy. Lower Level Needs are the kind of things you need to survive, so that would be like food, water, warmth and safety. Where as Higher level needs would be the kind of things you need to be fulfilled such as belongingness, esteem and self actualisation.
You'll find the Higher Level Needs are more common for making gangs than the Lower Level Needs and are most important at an early age which leads some criminologists to believe that it is a rejection of social norms that cause gang violence, be it hating the way people expect you to make money by not selling drugs you will think "no thanks mate" or if you need a good education that is not provided by the public education system you might turn to Gangs to make you money without the need for the tedious system in place.
Whichever way the cookie crumbles being in a low socio economic area is a perfect place for gang culture to develop and thrive. Be it because you need money for food and water leading you to steal and cheat; then joining the gang for ease of access or be it because you need to show society that you don't live by their rules so you decide to make money by selling drugs and preforming hits