It sounds funny but at one time there was literally a political party that referred to themselves as the "Know-Nothing Party" aka the "Order of the Star-Spangled Banner." They burned hot, they burned bright, they burned out. Their platform was essentially to oppose anything that wasn't white: Immigrants, Catholics, and Jews. This wasn't a new thing, since Germans, for whom English was not their primary language, and the Irish, who spoke accented English and were under suspicion of following not the rules and laws of the United States but instead the Pope and the Vatican. This was the height of mid-19th century "Nativism" - the idea that Native-born Americans (but most assuredly not Native Americans) were superior to literally everyone else.
They had secret societies whose sole platform was to oppose immigration to the United States. Anti-Catholic sentiment ran rampant. In the early 1830s posters around Boston exclaimed that "All Catholics and all persons who favor the Catholic Church are...vile imposters, liars, villains, and cowardly cutthroats." Samuel Morse, yes, the telegraph guy, wrote a bunch of articles in the New York Observer (he later published these articles in a book) just blowing that dog whistle that the Vatican was sending Catholics to the United States in order to undermine the government. He was popular enough to get nominated - but whooped - in the 1836 New York City mayoral election.
In August 1834, a group of anti-Catholics in Charlestown (just outside of Boston) - believing that nuns were being held against their will after which priests strangled the babies - stormed an Ursuline convent, chased out the eight nuns and 47 students, and proceeded to ransack it. John Buzzell, a brickmaker from New Hampshire:
The first thing that was done, after getting in, was to throw the pianos, of which nine were found, out of the windows. The mob crowded in such numbers that it was with great difficulty that I got upstairs to the chapel, which was located on the second floor. When I finally succeeded in forcing my way into the chapel I found a fire about the size of a bushel-basket blazing merrily in the middle of the floor. It was made of paper, old books, and such other inflammable stuff as they could lay their hands on, and soon spread in all directions. When the main building was enveloped in flames we went for the cook-house and ice-house, which were separate buildings, and set them on fire.
Buzzell went on to explain that he broke into the mausoleum, you know, to see if there were any dead girls whose deaths the priests were covering up. He said, and the aforementioned quote is from 53 years (not a typo) after the event, that he was sure there was a young nun named Mary St. John who was in the mausoleum that had not been dead for very long. Mary St. John, however, had testified against Buzzell in court - twice - so obviously he was extremely wrong.
It didn't stop people from believing the rumors, and it certainly didn't stop people from trying to profit off of them, either. In 1835, Rebecca Reed published "Six Months In A Convent," in which she claimed there was a plot to kidnap her and send her to the aforementioned Montreal convent. The following year Maria Monk published "Awful Disclosures of Maria Monk, or, The Hidden Secrets of a Nun's Life in a Convent Exposed," a sensational - and completely fabricated - account of her life in a Montreal convent in which a neighboring monastery's priests forced nuns into sex slavery. The book was promoted and likely written by William K. Hoyte and other nativists in New York. Hoyte was the super anti-Catholic head of the Canadian Benevolent Society who was sleeping with Monk. Published by the nativist James Harper in January 1836, it sold over 26,000 copies by July and over 300,000 copies by the time of the Civil War. Harper, the "Harper" in "Harper-Collins Publishing," was elected mayor of New York City in 1844.
1844 was also the year that anti-Irish sentiments exploded in Philadelphia. In May and July anti-Irish mobs attacked the homes of Irish-Americans, as well as Catholic churches. Zachary M. Schrag, a professor at George Mason, wrote that the riots "stand out for their duration, itself a product of nativist determination to use xenophobia for political gain." Philadelphia mandated singing Protestant songs and reading from the King James Bible in schools. A Catholic school director in Kensington, a northeast suburb of Philadelphia, floated in February 1844 suspending Bible reading in schools until the school board could come to a consensus regarding religion in schools for both Protestant and Catholic students. That went over about as well as you can imagine. Tensions simmered until they boiled over in May, when a teenaged nativist was shot and killed. A second person, who was just watching, died that day as well. Two days later nativists had burned a Catholic seminary and two Catholic churches. The rioting died down a couple of days later only after the U.S. Army and Navy had been sent in. Riots exploded again in July resulting in the deaths of at least 16 people.
This was the birth of the Know-Nothing Party, who peaked in 1856. That said in 1835 (the year after the Ursuline Riot) New York State's Native American Democratic Association, with support from the Whigs, who were anti-Andrew Jackson Democrats, gained 40% of the vote in the fall elections and, with that, momentum. By the 1840s the country's first true third-party had grown, with chapters in pretty much every major coastal city that had, like, immigrants and whatnot.
But where did the Know-Nothing Party get its name? Due to their origins with secret societies, if anyone was to ask them their platform, they were to respond "I know nothing." It was known that they did favor a 21-year residency requirement before citizenship could be considered, limiting alcohol sales (because, sure, the Irish and Germans were the only ethnic groups getting lit up in the United States), Bible readings in schools, and only allowing Protestants to teach school. As Lorraine Boissoneault wrote in the Smithsonian Magazine (linked above), "They were the first party to leverage economic concerns over immigration as a major part of their platform." Ahh, the long-mentioned "economic anxiety" that has plagued America for generations. Boissoneault explained that the Know-Nothings followed the typical pattern of nativist motivation: Nationalism, religious discrimination, and ethnic divisions stoked by politicians to appeal to the working class.
Two individuals in particular drove the Know-Nothing Party: A silversmith named Thomas Whitney and prizefighter/butcher William Poole. Whitney wrote the defining work of the Know-Nothing Party: "A Defence of the American Policy, As Opposed to the Encroachments of Foreign Influence, and Especially to the Interference of the Papacy in the Political Interests in the Affairs of the United States." As Whitney owned a printing press, he became the main publisher of Know-Nothing propaganda. And you most likely remember Poole as one of the main influences for Daniel Day-Lewis' character "Bill the Butcher" in Martin Scorsese's "Gangs of New York."
This came at a time when German and Irish immigration to the United States was exploding due to economic/political turmoil and a potato famine, respectively. 2.9 million people emigrated to the United States from 1845-1854, coinciding with the rise of the Know-Nothings. Over half of New York City was made up of foreign-born people. 70% of New York City's charity efforts involved Irish immigrants to the city. This simply couldn't stand. Whitney wrote that all people were "entitled to such privileges, social and political, as they are capable of employing and enjoying rationally." Essentially, as Boissoneault says, "only those with the proper qualifications deserved full rights."
The Know-Nothings picked up followers from the declining Whigs and enjoyed political success throughout the 1840s, they really gained steam ahead of the Kansas-Nebraska Act, in which slavery in those territories. By 1855 the governor of Massachusetts and all but two members of the Massachusetts state legislature were Know-Nothings, as well as 40 members of the New York state legislature, eight governors, 43 members of the House of Representatives, and five Senators. William Poole would die in 1855 after getting into a saloon fight with Irish boxer John Morrison and his men, one of whom shot Poole in the chest. Poole stuck around for almost two weeks before succumbing to his injuries. His last words were, "Goodbye boys, I die a true American." The Know-Nothings had themselves a martyr.
1856 was an election year, and the Know-Nothings aka the American Party were excited. But, like many other political groups at the time, they were splintered on the issue of slavery. There were enough abolitionists who still opposed immigration that their 1856 convention to nominate former president Millard Fillmore (with Andrew Jackson Donelson as his running mate) ended when the anti-slavery Know-Nothings left the convention. Fillmore and Donelson remained on the ballot.
The election came and with it one major final flashpoint, in Baltimore. It makes sense that Baltimore, or Maryland, would be the epicenter of the anti-Catholic sentiment, given that Maryland was originally founded as a safe haven for Catholics in the Colonies. Martin Ford wrote in Humanities that "election rallies were massive provocations, mixing theatrical spectacle with guerrilla warfare, Fourth of July pageantry with thuggery." Knowing that violence was likely, Maryland governor Thomas W. Ligon met with Baltimore Mayor Thomas Swann (a Know-Nothing man) to ensure that Swann would call off his gangs and allow everyone eligible to vote without fear of intimidation. Swann, in fact, did not do that.
On Election Day 1856, Baltimore had just 45 police officers for a population of almost 175,000 (up from 80,000 in 1830 thanks, in large part, to Irish and German immigration). The city, known as "Mobtown" thanks to the presence of political gangs, engaged in heavy-handed tactics to ensure their candidate was elected. One gang, the Blood Tubs, was so named due to their penchant for dumping tubs of fresh-from-the-slaughterhouse blood on voters who did not vote for their candidate. Other gangs kidnapped immigrants who didn't speak English off the street and take them to vote for their guy. New York's Empire Club came to Baltimore in 1856 to campaign for Democratic candidates, they were trapped in a house by the local Know-Nothings which led to a firefight using "small cannon and firearms." Not far away the Plug Uglies and the Rip Raps - both Know-Nothing gangs - engaged in a two-hour long volley of shots with a Democratic group that killed two. It's hard to get the exact figures, but one estimate had it at 30 dead and 350 injured.
Ligon wrote a report to the Maryland State Legislature in which he said that, "Party animosity ran riot throughout the city; the most desperate encounters took place, in which hundreds of infuriated partisans were engaged; arms of all kinds were employed; and bloodshed, wounds, and death, stained the record of the day...I retired from the scene, convinced that all this might have been prevented, and not without a painful sense of duty unfulfilled," also mentioning that Swann had abdicated his responsibility to ensure a free and fair election. Swann and the Know-Nothings would make further gains in 1858 before fading out.
Despite getting over 800,000 votes (about 21.5%) the Fillmore/Donelson ticket would go on to finish the 1856 election in a distant third place, with just eight electoral votes out of a possible 296. All eight electoral votes came from the state of Maryland. The dismal showing would mark the official end of the American/Know-Nothing Party. Ultimately, what with the growing threat of Civil War, America decided that slavery was a much more pressing issue than immigration. The Know-Nothings faded out just as quickly as they rose to prominence. The pro-slavery members of the party joined forces with the Democrats while the anti-slavery faction joined the emerging Republican party, and please do remember that the two parties switched platforms over the course of the next 100-ish years.
The nativist streak has been both in the background and in the forefront of American politics ever since. In 1882 Congress passed the Chinese Exclusion Act which...did exactly what it sounds like. Thirty years later Congress debated whether or not Italians were "full-blooded Caucasians" and whether or not immigrants from Southern and Eastern Europe were "biologically and culturally less intelligent" than their white counterparts. Just remember these events as you're watching the news terrified of a migrant horde streaming towards the border - they've been trying this for generations.