The refugees seeking haven in America were poor and disease-ridden. They threatened to take jobs away from Americans and strain welfare budgets. They practiced an alien religion and pledged allegiance to a foreign leader. They were bringing with them crime. They were accused of being rapists.

These undesirables were Irish.

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Fleeing a shipwreck of an island, nearly 2 million refugees from Ireland crossed the Atlantic to the United States in the dismal wake of the Great Hunger. Beginning in 1845, the fortunes of the Irish began to sag along with the withering leaves of the country’s potato plants. Beneath the auld sod, festering potatoes bled a putrid red-brown mucus as a virulent pathogen scorched Ireland’s staple crop and rendered it inedible.

While the potato blight struck across Europe, no corner of the continent was as dependent on tubers for survival as Ireland, which was mired in extreme poverty as a result of centuries of British rule. Packed with nutrition and easy to grow, potatoes were the only practical crop that could flourish on the minuscule plots doled out by wealthy British Protestant landowners. The Irish consumed 7 million tons of potatoes each year. They ate potatoes for dinner. They ate them for lunch. They even ate them for breakfast. According to Irish Famine Facts by John Keating, the average adult working male in Ireland consumed a staggering 14 pounds of potatoes per day, while the average adult Irish woman ate 11.2 pounds.

Through seven terrible years of famine, Ireland’s poetic landscape authored tales of the macabre. Barefoot mothers with clothes dripping from their bodies clutched dead infants in their arms as they begged for food. Wild dogs searching for food fed on human corpses. The country’s legendary 40 shades of green stained the lips of the starving who fed on tufts of grass in a futile attempt for survival. Desperate farmers sprinkled their crops with holy water, and hollow figures with eyes as empty as their stomach scraped Ireland’s stubbled fields with calloused hands searching for one, just one, healthy potato. Typhus, dysentery, tuberculosis and cholera tore through the countryside as horses maintained a constant march carting spent bodies to mass graves.

More than just the pestilence was responsible for the Great Hunger. A political system ruled by London and an economic system dominated by British absentee landlords were co-conspirators. For centuries British laws had deprived Ireland’s Catholics of their rights to worship, vote, speak their language and own land, horses and guns. Now, with a famine raging, the Irish were denied food. Under armed guard, food convoys continued to export wheat, oats and barley to England while Ireland starved.

British lawmakers were such adherents to laissez-faire capitalism that they were reluctant to provide government aid, lest it interfere with the natural course of free markets to solve the humanitarian crisis. “Great Britain cannot continue to throw her hard-won millions into the bottomless pit of Celtic pauperism,” sneered the Illustrated London News in March 1849. Charles E. Trevelyan, the British civil servant in charge of the apathetic relief efforts, even viewed the famine as a divine solution to Hibernian overpopulation as he declared, “The judgement of God sent the calamity to teach the Irish a lesson, that calamity must not be too much mitigated.”

Ireland’s population was nearly halved by the time the potato blight abated in 1852. While approximately 1 million perished, another 2 million abandoned the land that had abandoned them in the largest-single population movement of the 19th century. Most of the exiles—nearly a quarter of the Irish nation—washed up on the shores of the United States. They knew little about America except one thing: It had to be better than the hell that was searing Ireland.

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A flotilla of 5,000 boats transported the pitiable castaways from the wasteland. Most of the refugees boarded minimally converted cargo ships—some had been used in the past to transport slaves from Africa—and the hungry, sick passengers, many of whom spent their last pennies for transit, were treated little better than freight on a 3,000-mile journey that lasted at least four weeks.

Herded like livestock in dark, cramped quarters, the Irish passengers lacked sufficient food and clean water. They choked on fetid air. They were showered by excrement and vomit. Each adult was apportioned just 18 inches of bed space—children half that. Disease and death clung to the rancid vessels like barnacles, and nearly a quarter of the 85,000 passengers who sailed to North America aboard the aptly nicknamed “coffin ships” in 1847 never reached their destinations. Their bodies were wrapped in cloths, weighed down with stones and tossed overboard to sleep forever on the bed of the ocean floor.

Although most certainly tired and poor, the Irish did not arrive in America yearning to breathe free; they merely hungered to eat. Largely destitute, many exiles could progress no farther than within walking distance of the city docks where they disembarked. While some had spent all of their meager savings to pay for passage across the Atlantic, others had their voyages funded by British landlords who found it a cheaper solution to dispatch their tenants to another continent, rather than pay for their charity at home.

And in the opinion of many Americans, those British landlords were not sending their best people. These people were not like the industrious, Protestant Scotch-Irish immigrants who came to America in large numbers during the colonial era, fought in the Continental Army and tamed the frontier. These people were not only poor, unskilled refugees huddled in rickety tenements. Even worse, they were Catholic.

Conflict between Protestants and Catholics in the United States had already broken out in violence before the first potato plant wilted in Ireland. Anti-Catholic, anti-Irish mobs in Philadelphia destroyed houses and torched churches in the deadly Bible Riots of 1844. New York Archbishop John Hughes responded by building a wall of his own around Old St. Patrick’s Cathedral in order to protect it from the native-born population, and he stationed musket-wielding members of the Ancient Order of Hibernians to guard the city’s churches. Wild conspiracy theories took root that women were held against their will in Catholic convents and that priests systematically raped nuns and then strangled any children born as a result of their union.

The maltreatment of newcomers to the United States was, of course, hardly a cross for the Irish to bear on their own. However, while the number of German immigrants entering the United States nearly matched that of the Irish during the 1850s, the Irish were particularly vilified by the country’s Anglo-Saxon Protestants whose ancestors had explicitly made their exodus across the ocean to find a refuge from papism and ensure their worship was cleansed of any remaining Catholic vestiges. Feelings toward the Vatican had softened little in the two centuries following the sailing of the Mayflower. The country’s oldest citizens could still personally remember when America was an English colony and papal effigies were burned in city streets during annual Guy Fawkes Day celebrations.

Certainly, many Protestants reacted with Christian charity to the refugees. It was a Boston Brahman—Captain Robert Bennet Forbes—who spearheaded America’s first major foreign disaster relief effort by delivering food and supplies to Ireland aboard a government warship during “Black ’47.” In the new Irish exiles, however, many Protestants saw a papal plot at work. According to “Conspiracy Theories in American History: An Encyclopedia,” some Protestants feared the pope and his army would land in the United States, overthrow the government and establish a new Vatican in Cincinnati. They believed the Irish would impose the Catholic canon as the law of the land.

With immigration controls left primarily to the states and cities, the Irish poured through a porous border. In Boston, a city of a little more than 100,000 people saw 37,000 Irish arrive in the matter of a few years. Naturally, it was difficult to integrate the newcomers in such sheer numbers. The Irish in Boston were for a long time “fated to remain a massive lump in the community, undigested, undigestible,” according to historian Oscar Handlin, author of “Boston’s Immigrants, 1790-1880: A Study in Acculturation.”

The Irish filled the most menial and dangerous jobs, often at low pay. They cut canals. They dug trenches for water and sewer pipes. They laid rail lines. They cleaned houses. They slaved in textile mills. They worked as stevedores, stable workers and blacksmiths. Not only did working-class Americans see the cheaper laborers taking their jobs, some of the Irish refugees even took up arms against their new homeland during the Mexican-American War. Drawn in part by higher wages and a common faith with the Mexicans, some members of the St. Patrick’s Battalion had deserted the U.S. Army after encountering ill-treatment by their bigoted commanders and fought with the enemy. After their capture, 50 members of the “San Patricios” were executed by the U.S. Army for their treasonous decisions.

The discrimination faced by the famine refugees was not subtle or insidious. It was right there in black and white, in newspaper classified advertisements that blared “No Irish Need Apply.” The image of the simian Irishman, imported from Victorian England, was given new life by the pens of illustrators such as Thomas Nast that dripped with prejudice as they sketched Celtic ape-men with sloping foreheads and monstrous appearances.

In 1849, a clandestine fraternal society of native-born Protestant men called the Order of the Star Spangled Banner formed in New York. Bound by sacred oaths and secret passwords, its members wanted a return to the America they once knew, a land of “Temperance, Liberty and Protestantism.” Similar secret societies with menacing names like the Black Snakes and Rough and Readies sprouted across the country.

Within a few years, these societies coalesced around the anti-Catholic, anti-immigrant American Party, whose members were called the “Know-Nothings” because they claimed to “know nothing” when questioned about their politics. Party members vowed to elect only native-born citizens—but only if they weren’t Roman Catholic. “Know-Nothings believed that Protestantism defined American society. From this flowed their fundamental belief that Catholicism was incompatible with basic American values,” writes Jay P. Dolan in The Irish Americans: A History.

Buoyed by the war-cry “Americans must rule America!”, the Know-Nothings elected eight governors, more than 100 congressmen and mayors of cities including Boston, Philadelphia and Chicago in the mid-1850s. They found their greatest success in Massachusetts where in 1854 the American Party captured all state offices, the entire State Senate and all but a handful of seats in the House chamber. According to Dolan, once in power in Massachusetts the Know-Nothings mandated the reading of the King James Bible in public schools, disbanded Irish militia units while confiscating their weapons and deported nearly 300 poor Irish back to Liverpool because they were a drain on the public treasury. They also barred naturalized citizens from voting unless they had spent 21 years in the United States.

Millard Fillmore, the former president most notable for being un-notable, ran on the American Party’s 1856 presidential ticket. Throughout his political career, the 13th president had persistently courted the votes of nativist Yankees fearful of the changes brought by the Great Hunger refugees, and he blamed “foreign Catholics” for his defeat in the 1844 New York gubernatorial election. Although Fillmore finished third behind Democrat James Buchanan and Republican John C. Fremont, who had to swat down rumors that he was both a Catholic and a cannibal, the American Party received more than 20 percent of the popular vote and eight electoral votes.

In 1854, an anti-Catholic mob in Ellsworth, Maine, dragged Jesuit priest John Bapst—who had circulated a petition denouncing the use of the King James Bible in local schools—into the streets where they stripped him and sheltered his body in hot tar and feathers. That same year, the Know-Nothings in Bath, Maine, smashed the pews of a church recently purchased by Irish Catholics before hoisting an American flag from the belfry and setting the building ablaze. When the bishop of Portland returned to the city a year later to lay a cornerstone for the church’s replacement, another mob chased him away and beat him.

The violence turned deadly in Louisville, Kentucky, in August 1855 when armed Know-Nothing members guarding polling stations on an election day launched street fights against German and Irish Catholics. Immigrant homes were ransacked and torched. Between 20 and 100 people, including a German priest fatally attacked while attempting to visit a dying parishioner, were killed. Thousands of Catholics fled the city in the riot’s aftermath, but no one was ever prosecuted for crimes committed on “Bloody Monday.”

A Know-Nothing mob even seized a marble block gifted by Pope Pius IX for construction of the Washington Monument and tossed it in the Potomac River. A pamphlet published by Baltimore’s John F. Weishampel suggested that the stone could be used as a signal from the pope to launch an immigrant uprising to take over America. “The effects of this block, if placed in the monument, will be a mortification to nearly every American Protestant who looks upon it,” he warned, “and its influence upon the zealous supporters of the Roman hierarchy will be tremendous—especially with foreigners.”

Abraham Lincoln was among the many Americans disturbed at the rise of the nativist movement as he explained in an 1855 letter: “As a nation, we began by declaring that ‘all men are created equal.’ We now practically read it ‘all men are created equal, except negroes.’ When the Know-Nothings get control, it will read ‘all men are created equal, except negroes and foreigners and Catholics.’ When it comes to this I should prefer emigrating to some country where they make no pretense of loving liberty—to Russia, for instance, where despotism can be taken pure, and without the base alloy of hypocrisy.”

The good news for Lincoln and those Americans with similar views is that the Know-Nothing Party cratered quickly after reaching its high-water mark, although nativism has proven to be stubbornly persistent. The party splintered as the slavery question superseded the immigrant menace with flashpoints such as the Kansas-Nebraska Act, the Dred Scott decision and the uprising at Harper’s Ferry steering the country to armed conflict.

Although stereotyped as ignorant bogtrotters loyal only to the pope and ill-suited for democracy, and only recently given political rights by the British in their former home after centuries of denial, the Irish were deeply engaged in the political process in their new home. They voted in higher proportions than other ethnic groups. Their sheer numbers helped to propel William R. Grace to become the first Irish-Catholic mayor of New York City in 1880 and Hugh O’Brien the first Irish-Catholic mayor of Boston four years later.

A generation after the Great Hunger, the Irish controlled powerful political machines in cities across the United States and were moving up the social ladder into the middle class as an influx of immigrants from China and Southern and Eastern Europe took hold in the 1880s and 1890s. “Being from the British Isles, the Irish were now considered acceptable and assimilable to the American way of life,” Dolan writes.

No longer embedded on the lowest rung of American society, the Irish unfortunately gained acceptance in the mainstream by dishing out the same bigotry toward newcomers that they had experienced. County Cork native and Workingmen’s Party leader Denis Kearney, for example, closed his speeches to American laborers with his rhetorical signature: “Whatever happens, the Chinese must go.”

Kearney and the other Irish failed to learn the lesson of their own story. Yes, the Irish transformed the United States, just as the United States transformed the Irish. But the worst fears of the nativists were not fulfilled. The refugees from the Great Hunger and the 32 million Americans with predominantly Irish roots today strengthened the United States, not destroyed it. A country that once reviled the Irish now wears green on St. Patrick’s Day. That’s something to raise a glass to.