New York City
Organized crime has long been associated with New York City, beginning with the Forty Thieves and the Roach Guards in the Five Points in the 1820s. The 20th century saw a rise in the Mafia, dominated by the Five Families, as well as in gangs, including the Black Spades. The Mafia presence has declined in the city in the 21st century.

Q: What group controlled the Mafia in New York in the 20th century?
the Five Families