Apparently, a drought created the mafia. That’s not my opinion, but it is the findings of research published by the Center for Economic Policy Research.
They found that a popular leftist movement flourished in Sicily in 1893 during an intense drought. The mafia was supported by multiple interests on the right to counter to this group. By 1900, areas with the largest political activity in 1893 became strongholds for the Cosa Nostra.
The paper has a lot of other findings, but none of them are nearly as interesting. If it wasn’t published by actual scientists, I would think it was a wonderful example of a spurious correlation.