IMO, the long term trend in American Mafia has been the transition from Cosa Nostra to Cosa Mia. A big part of it is drugs: defiance by guys on the street of the Dons' "ban" on drug-dealing, and their selling out of higher ups when caught in return for shorter sentences. I don't think drugs, by themselves, have been the ruination of the Mob as Vito predicted. But they did contribute strongly to the Mob's decline.