It used to be because of rivalries exacerbated by systemic racism, literal segregation, and a burgeoning drug trade.
All races in the US had street gangs with similar ferocity and reckless nihilism.
It cooled off, and the literal segregation was replaced by a forged economic segregation.
There is not a need or a reason for gangs, and they are no longer a product of White supremacy, but purely exist due to the failure of two generations to eradicate them from their environment. "OGs" are the reason gangs still exist, they glorified, maintained, and then attempted to place their existence on the "feds."
Chicago guys took it to the extreme, and almost exclusively terrorize Black neighborhoods.
I heard someone say that the cops dropped guns off in Black neighborhoods.
My question is why did they immediately start shooting each other with them?