The Supreme Court gutted Chicago's plan to control gun violence.
It used to be illegal to keep or carry a gun in Chicago without a special permit. Anyone stopped carrying a gun, was charged with a felony.
This largely worked because gang members and other criminals only carried guns for brief periods when then expected to need them and they also assumed that others would be unarmed. When arguments arose, they resulted in fist fights or knife injuries which were usually survivable.
When someone robbed a store, they might hit the clerk in the face with the butt of a gun, but there was no need to shoot him, because he was not going to shoot first.
When the Supreme Court decided that the rights of individual's to keep and carry guns for supposed self defense were more important than the safety of the larger population, guns flourished and gun crimes shot up.
No one has figured out how to put the genie back in the bottle. The same gangs are still around and the same criminals, but now they are all armed.