FACTBOX: Who are the 'Ndrangheta

(Reuters) - Six Italian men were shot dead in the German city of Duisburg on Wednesday in an execution-style killing linked to a mafia feud.

Italian Interior Minister Giuliano Amato said the shootings appeared to be linked to a feud between two mafia clans in the southern region of Calabria, home to the 'Ndrangheta organized crime group.

Here are some key facts about the group:

* ORIGINS:

-- The Calabrian "Honoured Society", known as "'Ndrangheta", in the Calabria region of south Italy is the equivalent of the Sicilian Mafia.

-- 'Ndrangheta began as a defense network for impoverished rural peasants against aristocratic landlords. Members emigrated to Canada and the United States, and were discovered running an intimidation scheme in Pennsylvania mining towns in 1906.

* HOW DOES IT WORK?

-- They are known as "The Honoured Society", Fibbia or Calabrian mafia. Instead of the pyramid structure of bosses used by other mafia, The 'Ndrangheta" uses families based on blood relationships, inter-marriages, or being a Godfather. Each group is named after their village, or after the family leader.

* TWENTIETH CENTURY EXPANSION:

-- When Calabria began the process of industrialization and urbanization in the late 20th century, the 'Ndrangheta became interested in drug trafficking, weapons sales and public works and construction.

* THE PRESENT:

-- In 2004, authorities uncovered an international drugs trafficking network involving gangs in South America, Australia, and Europe. Drugs from Colombia were destined for countries such as Greece and Bulgaria.

-- Italian officials estimated at the time that 80 percent of Europe's cocaine had arrived from Colombia via Gioia Tauro's docks in Reggio Calabria.

-- Italian anti-organized crime agencies have estimated that the 'Ndrangheta earns about $30 billion annually, mostly from illegal drugs, but also from ostensibly legal businesses such as construction, restaurants and supermarkets.

-- There are believed to be about 100 'Ndrangheta families in Calabria, who have become more successful than their Sicilian counterparts because their family ties are closer.

Sources Reuters//www.ndrangheta.org/ www.americanmafia.com