Mafia is nothing more nothing less than organized crime. Any country has it. In china they call it 黑手党， in Japan Yakuza and so on. It just happen that italian mafia has been depicted in so many movies (all americans) and has been under the spotlight for many years. Being an italian I think mafia today in order to survive, has strong links with politicians, high ranked officials, that's the only way to get their dirty hands pretty much everywhere.