Furio, 80% of all Italian Americans came from Naples down to Sicily. I believe there is some rivaly between Neapolitans and Sicilians, but there is actual animosity between Northern Italians and Southern Italians. The dialect is even more different between North and South. The Mafia in Italy has its roots in Sicily, Naples & Calabria, all in the South.
In America, there is a good mixture of American Mafioso who are from Naples down to Sicily:
Al Capone, Southern Italian
Frank Nitti, Southern Italian
Paul Ricca, Southern Italian
Tony Accardo, Sicilian
Sam Giancana, Sicilian
Joey Auippa, Sicilian
Jack Cerone, Southern Italian

Carlo Gambino, Sicilian
Vito Genovese, Southern Italian
Joe Bonnano, Sicilian
Salvatore Maranzano, Sicilian
Lucky Luciano, Sicilian
Joe Masseria, Southern Italian
John Gotti, Southern Italian