"Underbelly" refers to the vulnerable or hidden part of a person, organization, or society that is often associated with negative or illegal activities. Full definition
The scene around Greenberg was open to that kind of black underbelly of America. (bombmagazine.org)
Plea bargaining is the dark underbelly of criminal justice. (suttonhart.com)
The former dances the line between science fiction and horror in Nowheresville, Indiana and the latter tells a story of schlock and excess in the seedy underbelly of Los Angeles. (relevantmagazine.com)