First rackets begun in Sicily in 1750's. When criminals moved to USA alongside other Italian immigrants, they continued the practice. They concentrated on Italian immigrants in cities like New York, Chicago and San Francisco. Possibly as much as 90% of Italian immigrants in New York were threatened.
Typical Black Hand tactics was to send a letter to a victim threatening bodily harm, kidnapping, arson or murder. Letter demanded a specified amount of money delivered to a specific place. It was "decorated" by threatening symbols like a smoking gun or hangman's noose and signed with a hand imprinted in black ink; hence the name La Mano Nera (The Black Hand).
Gangsters did carry out the threat if the victim did not pay. Ignazio Saietta, gangster in New York's Little Italy, strangled his victims and burned the bodies. One of the threatened victims was the tenor Enrico Caruso. In occasion, Black Handers threatened other gangsters and usually faced retaliation.
If the law enforcement closed in, gangster answered with their usual style; assassination. Victims include New Orleans police chief Daniel Hennessy and NYPD lieutenant Joseph Petrosino. They intimidated potential witnesses even in the court room.
Black Hand practice practically disappeared when gangsters found a more profitable enterprise; bootlegging during the US Prohibition.