Immigration rates fell dramatically during the first two decades of the nineteenth century, as restrictions on shipping during the Napoleonic Wars and the War of 1812 blocked the flow of migrants from Europe to America. After 1820, however, immigrants once again began flooding into America at an ever-increasing rate; 150,000 newcomers arrived in the 1820s, 600,000 in the 1830s, 1.7 million in the 1840s, 2.6 million in the 1850s.14
By the 1840s, the migrant stream included large numbers of Roman Catholics from Ireland and Germany. Many of America's native-born Anglo-Saxon Protestants despised the Irish—whom they regarded as a separate and inferior race—and feared that Catholics would undermine American democracy by slavishly voting according to the dictates of the Pope, the spiritual and organizational leader of the Roman Catholic church. In 1860, the Census Bureau found that Roman Catholicism had become the largest single religious denomination in the United States, a development attributable almost entirely to immigration.
By 1850, 10% of the American population was foreign-born, and nearly half of those immigrants were Irish.15 Native-born inhabitants of cities like Boston and New York—where Irish immigrants settled in disproportionate numbers and began to exercise political power—feared an Irish Catholic takeover of their communities. In 1849, native-born Protestant workingmen in New York City founded a secret society called the Order of the Star-Spangled Banner to fight against Catholics and immigrants in defense of traditional American values. Its members swore an oath of secrecy, promising to respond to any questions about the Order by replying, "I know nothing." They have been known ever since as "Know-Nothings."
The Know-Nothing movement rapidly spread through the country in the early 1850s. The rise of the Know-Nothings corresponded with the collapse of the established two-party system; when the old Whig Party disintegrated, it appeared for a brief moment that the Know-Nothings might rise to become the main party of opposition to the ruling Democrats (who drew support from immigrant political machines like New York's Tammany Hall). The Know-Nothings sought not to stop immigration but rather to limit immigrants' ability to participate in the political life of the nation. The Know-Nothings' platform, adopted in 1854, called for a 21-year waiting period for naturalization, an outright ban on immigrants holding elective office, a ban on Catholic teachers in the public schools, and prohibition of drinking (which was regarded as a particularly Catholic vice).
The Know-Nothings' platform resonated with native-born voters in northern cities with heavy immigrant populations. In 1854, Know-Nothings won control of major cities (Boston, Philadelphia, Washington, and San Francisco) and entire state legislatures (Massachusetts, Pennsylvania, Maine, Indiana, and California). More than 90 congressmen claimed Know-Nothing backing.
Within just a few years, however, the Know-Nothing movement began to peter out. Northern voters came to view the threat of slavery as more dire than the threat of immigration; the new, antislavery Republican Party displaced the Know-Nothings' American Party as the main opposition to the Democrats. Abraham Lincoln, a young Republican legislator in Illinois, offered perhaps the most eloquent repudiation of Know-Nothing politics. "I am not a Know-Nothing," he wrote. "How could I be? How can any one who abhors the oppression of Negroes be in favor of degrading classes of white people? Our progress in degeneracy appears to me pretty rapid. As a nation we began by declaring '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 example, where despotism can be taken pure and without the base alloy of hypocrisy."
In 1856, the Know-Nothings ran ex-President Millard Fillmore as their candidate for president. Fillmore's weak showing—he garnered just 22% of the vote, running a distant third to Democrat James Buchanan and Republican John C. Fremont—marked the end of the Know-Nothings as a major force in national politics.