David Bernstein and Noah Isackson have a pretty good article in Chicago Magazine, Gangs and Politicians in Chicago: An Unholy Alliance. Focusing mainly on Alderman but also including State and Federal legislators, they assert that “gangs” provide the money, votes, and workers that enable officials to attain and retain their office. In exchange, the governments these legislators control provide funds and favors.
Isackson and Bernstein stop short of suggesting how to repair this problem, but reading thru the article it’s clear that the main way these “gangs” prosper is thru unauthorized distribution of drugs. And one of the main favors aldermen provide is assistance in avoiding “law enforcement” efforts to arrest them. End the drug prohibition, most of the “gangs'” income will end, and candidates will no longer get “gang” money. They’ll have to rely on crooked lawyers, lobbyists, etc.
Some of the drug money, of course, has gone into real estate, with “gang” members able to get favors such as rezoning and inspection waivers. A land value tax, by constraining real estate speculation, would be of assistance here.