As late as 1850, the two party system was, to all outward appearances, still healthy. Both the Democrats and Whigs were able to attract support in every section and neither party was able to win more than 53 percent of the popular vote. Then, in the space of just five years, the two-party system disintegrated in response to two issues: foreign immigration and the reemergence of the issues of slavery expansion.
A massive wave of immigration from Ireland and Germany after 1845 led to an outburst of anti-foreign and anti-Catholic sentiment. Between 1846 and 1855, three million foreigners arrived in America. Nativists--ardent opponents of immigration--capitalized on deep-seated Protestant antagonism toward Catholics and working-class fear of economic competition from cheaper immigrant labor. Nativists charged that Catholics were responsible for a sharp increase in poverty, crime, and drunkenness, and were subservient to a foreign leader, the Pope.
In 1849, native-born Protestant workingmen formed a secret fraternal organization, "The Order of the Star-Spangled Banner," which became the nucleus of a new political party known as the Known-Nothing or American party. The party received its name from the fact that, when members were asked about the party's workings, they were supposed to reply, "I know nothing."
The Know Nothings attracted support not only from nativists, but from large numbers of northern free soilers and southern Whigs. By 1855, the party had captured control of all New England except Vermont and Maine and was the dominant opposition party to the Democrats in New York, Pennsylvania, Maryland, Virginia, Tennessee, Georgia, Alabama, Mississippi, and Louisiana. The party platform included a 21-year residency period before immigrants could become citizens and vote, limitations on office-holding to native-born Americans, and restrictions on the sale of liquor.
One Northerner who spoke out against the Know Nothings was Abraham Lincoln, who eloquently argued that the party's nativist platform was a violation of the country's republican principles.
I am not a Know-Nothing. 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.