> Like the family in A Tree Grows in Brooklyn, more than 36 million Americans trace their ancestry to Ireland according to a 2008 survey. The Irish played a major role in settling the American South, and the influx of immigrants into cities like New York City, Boston and Philadelphia in the 19th century helped shape the industrial North.

> The major impetus for emigration to the United States was the Great Irish Famine that lasted from 1845 to 1852. The spread of the potato blight affected all of Europe, but was particularly devastating in Ireland, where potatoes were a major food source. Adding to the problem was British control of the country and widespread limits on the rights of Irish Catholics. At times they were not allowed to vote, own land, own firearms or attend school. When bans on education were lifted, the British set up a national school system that forced Irish children to learn English rather than Gaelic and study British history and literature. To escape these restrictions, many Irish men and women fled to the United States, settling largely in port cities because they did not have the money to move inland after paying their boat fare. By 1910, there were more Irish people in New York City than in Dublin.

> These new American citizens were largely uneducated. As a result, many of them found work in factories or as domestics. None of these jobs paid well, leading to widespread poverty and discrimination. Over time conditions would improve, primarily among those who invested in education. By the early 20th century, when A Tree Grows in Brooklyn is set, education was helping many Irish-Americans move into more prosperous jobs, with earnings on a par with any other Americans. Families like the Nolans were increasingly in the minority, and the film and novel make it clear that their poverty is a result of Johnny Nolan's drinking and his inability to hold a steady job. With Johnny and Katie pushing their children to get better educations, the new generation's lives promise to be more secure than their parents'.