I think that "mafia" is a metaphore for all organised crime.

Organised crime exist is every country and in every city.

The "real" mafia still comes from Sicily, basta. Altough there are more organisations that we all call Mafia. Russian's, Japanese, Colombians etc.

Corleone rules the world, Not the US of A, not Russia. The BOSS sits in the town of Corleone and he reigns the world.