"Out of Ireland" opens with a letter written in 1870 by Maurice H. Woulfe to his brother Michael. Maurice composed his letter from an Army barracks in the Wyoming Territory. Michael received it in Cratloe, County Limerick, Ireland. Maurice provided an upbeat account of life in America, but then confided, "I can never forget home, as every Irishman in a foreign land can never forget the land he was raised in. Every stone, gap, and field in Cratloe and its surroundings are as clear in my mind as when I was home. …"

Miller says Maurice Woulfe is one of about seven million individuals who departed Ireland for America during the 18th, 19th and 20th centuries. Some found the new life miserable. Others found it joyous. Most fell in between those extremes. But it seems almost all of them spoke paradoxically, sooner or later, sounding something like Woulfe: "I was never better in my life" but "in spite of all I can never forget home."

The research conducted by Miller has far-reaching implications. After all, about 40 million current residents of the United States trace all or part of their ancestry to those seven million immigrants. As for the mirror image, almost every one of Ireland's current five million inhabitants is related to somebody living in the United States.

Between 1841 and 1926, the population of Ireland fell by half, from about 8.5 million to only 4.25 million. Many Irish blamed what they perceived as Ireland's social stagnation and cultural conservatism on the drain of vibrant men and women. For the United States, however, Irish immigration turned out to be mostly positive. The Irish helped develop farms, cities, industries and a transportation network, foundations of American prosperity.

Yet pictures in the documentary are not always pretty: "Today, Irish Americans enjoy higher social status and greater wealth and influence than almost any other ethnic group. But the long history of Irish immigration is tinged with sadness, anger and even tragedy." Some felt driven out by British tyranny or landlord oppression. Once in the United States, many immigrants, more often the Catholics than the Protestants, battled overt discrimination.

After completing the movie, Miller and Wagner followed with a book of the same title. Like the movie, it is derived partly from Miller's unmatched collection of memoirs and letters written by and to Irish immigrants in the United States. Pleased with the popularization, Miller decided to continue in that vein while simultaneously writing for fellow academics. In 2001, for example, he and his wife, Patricia Mulholland Miller, published an illustrated book, Journey of Hope: The Story of Irish Immigration to America (Chronicle Books, 2001). The book includes hands-on, interactive elements (such as letters that unfold after being removed from sealed pouches). Meanwhile, Miller worked on the scholarly follow-up to Out of Ireland.

He envisioned the book as a tome presenting the former book's complete, unedited memoirs and letters, each accompanied by a detailed interpretation. The task was so mammoth that Miller collaborated with three other scholars -- Arnold Schrier, Bruce D. Boling and David N. Doyle. Oxford University Press published the finished work, Irish Immigrants in the Land of Canaan: Letters and Memoirs From Colonial and Revolutionary America, 1675-1815, late last year.