The United States shows how migrants often take their own model of a secret society with them. The fraternity derived from English Freemasonry, publicly known yet secret, was particularly popular. From the mid-nineteenth until well into the twentieth century, some tens of millions of men (and far fewer women) were members of fraternal orders, which as a matter of fact often also functioned as insurance companies. Among the numerous new organizations that sprang up after the Civil War was the Ku Klux Klan (from the Greek kuklos, circle), founded in Tennessee in 1866, but disbanded after a few violent years. In part as a result of the success of Birth of a Nation, the movie by D.W. Griffith, the Klan was resurrected in 1915 and, after the US entered WW I, evolved into a militant white enemy of Catholics, Blacks, Jews, strikers, and others deemed un-American. In the mid-1920s it counted some 3 million members, but by the end of the decade membership was closer to 100,000, and the mass movement dwindled to a sect.
The Irish migrants to the coal fields of Pennsylvania in the mid-nineteenth century imported a different tradition. Since 1760 the Irish countryside had had underground organizations, whose members were over time called Whiteboys, Ribbonmen, or Molly Maguires, who were engaged in intermittent fights against the landowners. In Pennsylvania, amid the more skilled English and Welsh miners, the Irish clearly were at the bottom of the social scale. When they tried to defend themselves against deteriorating labour conditions after the Civil War, their old organizational traditions resurfaced in the framework of the local lodges of the Ancient Order of Hibernians, an Irish-American brotherhood that normally followed the English pattern. Economic developments, efforts to establish a trade union, tensions among the Catholic Irish due to the Church's aversion to secret societies, the customary toughness of the mining region - these and other elements contributed to a growing climate of violence, for which the Molly Maguires were blamed. The Philadelphia & Reading Railroad, which had acquired many of the mines, hired the Pinkerton Detective Agency, one of whose agents, James McParlan, infiltrated the group under the alias of McKenna. From the mid-1870s, this resulted in arrests, trials, and 20 death sentences. For Allan Pinkerton, the Mollies were part of a success story that gave his agency a name and provided the material for a sensational book.
Read also McKenna's initiation into the Molly Maguires (Pdf 128 Kb).
Source: Allan Pinkerton, The Molly Maguires and the Detectives (= Allan Pinkerton's Detective Stories, vol VI), new and enlarged ed., New York etc.: G.W. Carleton, 1881, pp 134-145. (Call number: US210/15).