This is my theory, based on history lessons, and not using AI for this theorem.

In my opinion, COsa Nostra in Italy emerged because the old roman emperors, as early as Caligula, and after him basically every emperor in power, was paying the praetorians money to protect him and do his dirty work against the roman senate. Over the centuries, this stuck as racket money and as cosa nostra. Basically this corrupt mechanism of buying protection from a personal guard army like the praetorians in order to stay in power, gave rise to the Cosa Nostra.

This habit of buying protection gave rise to the praetorians to self-organize into a mafia