"Instead of fighting old enemies, when it was the Hatfields and the McCoys, now it's the McCoys and the McCoys," says Andrew Papachristos, a sociology professor at Yale University who has studied gangs in Chicago. "Gangs are no longer hierarchical. They are now much more elusive and complex."
Added to the mix – and no doubt raising the stakes – is the illicit drug trade. Chicago is the distribution hub for the Midwest, and its street gangs operate almost like corporate distributors for the Mexican cartels, say officials and criminologists. Four major cartels – Sinaloa, Los Zetas, Juarez, and Tijuana – have extended their networks into the Great Lakes region, according to the 2011 National Drug Threat Assessment from the Justice Department's National Drug Intelligence Center.