The answer to your question depends on what you mean when you say ‘Italian Mafia’ because there are several criminal organizations which can lay claim to the name. In Italy you have La Cosa Nostra, Camorra, ‘Ndraghetta, Stidda, and Sacra Corona Unita. All of these groups are organized crime elements in the country. And in America you have several mafia families dotted across the nation.

The Camorra and ‘Ndragheta are the oldest of the organizations, with the Camorra having its origins as a secret society back in the early 1700s and the ‘Ndragheta being used to describe violent youths in Calabria in the late 1700s. The Stidda and Sacra Corona Unita are relatively new organizations having been established in the 1980s due to the Mattanza - or The Slaughter - that was a mafia war in Italy taking place in the 1970s to 1990s. Interesting side note, the originators of the Mattanza were the Corleonesi clan, a group originating in the rural town of Corleone.

But I’m going to assume that you’re asking about either the Sicilian Mafia - La Cosa Nostra - or the American Mafia. Both of which are much more well-known than their counterparts.

You’ve got two groups that led to the creation of the Sicilian mafia: the gabellotto (or gabellotti) and the cosche. The gabellotto were a sort of middleman in Italy. Aristocrats in Sicily were absentee landlords. They owned a bunch of rural farmland but they mostly wanted to stay in the cities. So the aristocrats would lease out their land to gabellotto who would then parcel out the land to peasants to work it. Being a gabellotto actually provided some measure of social mobility for the poor and unlanded peasants. Anton Blok, in an article called 'Peasants, Patrons, and Brokers in Western Sicily' provides an example of a man who "rose to wealth as a gabellotto, acquired land and noble title (baron) married a rich landowning duchess and consequently settled in the city of Palermo, leaving the administration of his estates (leased to gabellotti) to his cousin who regularly went on horseback to Palermo to deliver the gabella. His only daughter inherited seven latifundia and married a baron."

The gabellotto would often hire a bunch of armed young men to protect the land he was leasing from the aristocrats. These young men often had experience as cattle rustlers or bandits. And, along with the rent the gabellotto would charge the rural peasants, he would also collect pizzo - or protection money - from people around his land.

You also had the cosche. Because there was no real police force in Sicily, you had individuals who would band together to protect their villages or their people. These were the cosche. Selwyn Raab, in his book The Five Families, explains that the cosche "evolved from guerrilla-like, disorganized bands for self-defense into greedy, terrifying gangs."

Cosche originally acted as protectors and a proto-police force but soon devolved into violent gangs. When Sicily was absorbed into Italy in the 1860s, the Italian government didn't know how to overcome the bandits causing disorder on the island. The more organized cosche made a deal with the new government of Rome where they would put down these gangs and Rome would allow them to operate at will. Even the Catholic Church bent to the will of the cosche. Raab explains that the Catholic Church relied on the mafia "to safeguard its vast land holdings on the island and to stifle peasant demand for land or for larger payments as tenant farmers. Grateful for the protection, church leaders refrained from denouncing the mafiosi's strong-arm tactics."

As far as how one would become a member of the mafia, it was relatively easy in Sicily. Bernardino Verro, a socialist mayor of Corleone, had deep ties with the local mafia - the Fratuzzi. Wanting to get the mafia on the socialists' side in order to provide protection for labor strikes, he joined up with them in a secret ceremony. He wrote that "I was invited to take part in a secret meeting of the Fratuzzi. I entered a mysterious room where there were many men armed with guns sitting around a table. In the center of the table there was a skull drawn on a piece of paper and a knife. In order to be admitted to the Fratuzzi, I had to undergo an initiation consisting of some trials of loyalty and the pricking of the lower lip with the tip of the knife: the blood from the wound soaked the skull."