Gets,

The cause of violence varies from location to location. Let me explain through a historic lens.

Chicago have an extensive gang history going back to the early 1900s of course with variety of European gangs then later blacks, latinos and asians will emerged. The cause of violence back then is similar today with protecting the neighborhood but also racketeering. The gang scene was tremendous then with 1,300+ gangs in the city around 1927 compared to 50+ today. The prohibition era gang wars cause many casualties and Chicago ended 1928 with 498 murders for example. During these times the gangs census was predominately white.
As years progress pass both World Wars, the demographics began to change in certain neighborhoods and Blacks & Latinos grew significantly. This affected the gangland and more gangs would emerge from the black & latino communities due to white gangs harassing, assaulting, and or killing minorities. The 50s & 60s was the era that certain gangs became generational and later get involved in the drug trade/rackets.
The violence between the 50-60s was mainly local rivals within the immediate area, alliances formed, and later the concept of "Nations". The 70s intensified the fueling with heroin street market becoming pervasive and the end of the 70s the Folks/People (6/5) alliance started behind bars.
The 80s was make and break years and census changing from majority white to black/latino due to white flight. Hence why some white gangs went extinct and others mix ethnicity ( Royals, Deuces, Gents, etc half/majority latino). The 6/5 push/pull different nations together (except Black Souls/ New Breeds) which mean instead of having beef with the 1 or 2 groups now due to the 6/5 your rivalry extended to 10-11 groups even if your nowhere near their turf. Coke & later crack trade involvement.
The 90s saw the internal allies war and certain gun lines becoming semi-permanent, tearing down the high rise begun, leadership of the Big 4 orgs being indicted, money cliques start up.
Since then there have been more indictments, internal leadership rebellions, Decks (equivalent of a crew) flipped to other orgs or completely renegade, youngsters being impulsive.

Take all this historic politics and internal conflicts and localized it to certain blocks and districts and that's what we have today. The hierarchy overall didn't collapse with the projects but certain leadership collapse in some decks more than others. It get to point where you have to dig to separate feuding over petite causes from business. There was never a single top dog.