In studying issues of immigration in the United States I think it is interesting to note that while it would take another 30 years for immigration restrictions to come to a stronger central role that much of the early decades of the 1800s focused in on the arrival of the Irish.
These Irish were not middle class or rich generally. They were not as rural as once believed but for the most part they were moving on mass (about 2 million between 1830-1860). This group were moving because of the effects of the potato famine of the 1840s. In 1845, as the Latter Day Saints were preparing to head west the Irish potato crops began a six year failure.
This failure destroyed one of the most important sources of food for the Irish poor. It forced them out as much as the luwer of America drew them. With them they brought Catholicism.
While there was Catholics and Irish in the USA prior to the 1830s they were a small insignificant minority. After 1850 the number of Catholics in the Urban centres of Philadelphia, Boston and New York saw the growth of anti Popery in the minds of the Protestant majority.
Novels and so called true accounts of the scandals of Catholics in Montreal and elsewhere tantilized and terrorized citizens of the period. Awful Disclosures of Maria Monk, or, The Hidden Secrets of a Nun’s Life in a Convent Exposed was written in 1836 and became hugely popular. The book portrays a good Protestant girl who is later brought up Catholic, becomes a Nun and finds out that all sorts of terrible things happen in nunneries.
It is effective and terrible false Victorian Porn. The success of this book, coupled with the anti-Catholic movement of preachers in Antebellum America led to riots against Catholics, mostly Irish. They attacked their churches during the last year of Joseph Smith’s life. Killing some Catholics in the process.
All of this violence led eventually to the establishment of the Knownothings (Nativists) party which was almost wholely anti-immigrant. They were especially hostile towards the influx of mass Catholic migrations from Ireland and Germany.
It is interesting as you look at this history how it similar the tactics of Anti-Popery was to Anti-Mormonism. The mob violence followed with semi-official repression seems to be the major resource of the day. For decades after their arrival Irish Catholics were treated as second class citizens often considered easily swayed into criminal activity. Often they were seen as little better than Slaves.
As a Mormon I can certainly sympathise with their plight in that period.