Metro Specific Underworld

Underworlds are ethnic. It says so right here. Furthermore, the ethnic underworld in effect is specific to the American locale of the setting.

The UK has the inescapable London Gangster, as well as The Yardies to add some ethnic flavour. Russia has its own Mafiya, Hong Kong of course has the The Triads and the Tongs, and Japan has the infamous Yakuza. See Generic Ethnic Crime Gang for the Honorable Mentions - gangs not pervasive enough to have their own tropes yet.