DPN, that isn't correct.

The maffia was founded in north-west Sicily, around 1857-1860.
In 1890, the maffia was already a very powerful organisation that controlled the whole country of Sicily.

If it is true that there were already mafiosi in New Orléans in the 1860's, then those mafiosi left Siciliy directly to establish the maffia there too.

Anyway, the maffia was founded because Sicily was the largest exporter of Citrus-fruits (oranges, lime, lemon) in the world. They exported especially to the USA. So those mafiosi in New Orleans probably wanted to be on the other side of the Citrus-connection too, to be sure they controlled every aspect of it.

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See, we can act as smart as we want, but at the end of the day, we still follow a guy who fucks himself with kebab skewers.