In the nineteenth century, the term "nativism" referred to white, native-born, Protestant Americans' hostility to European immigrants. Since many of those immigrants prior to the Civil War were Roman Catholics, ethnic prejudice against immigrants was usually accompanied by visceral hatred of Catholics as well. Indeed, because Americans had overtly identified themselves as a Protestant, anti-Catholic nation since the seventeenth century and because prominent Protestant clergymen had warned since the early nineteenth century of a Papal plot to subvert American liberty and seize control of the United States politically through the use of slavish Catholic immigrant minions, waves of new European immigration which spawned outbursts of nativist sentiment also provoked anti-Catholicism. Immigration from England, Ireland, and Germany — as well as Canada and other European nations — was constant throughout the nineteenth century, but it especially swelled between 1845 and 1855 as immigrants fled famine, poverty, and political turmoil in Ireland and Germany.

Nativism took a variety of forms. Middle-class and elitist gentlemen, who sniffed that socially inferior immigrants lacked the intelligence and experience to be good republican citizens, occasionally gathered in exclusive nativist fraternities such as the Order of United Americans or the United Sons of America. But when immigration coincided with hard times, as it did in the late 1830s and early 1840s and especially in the mid-1850s, and/or with periods of political discontent, then the charges advanced against immigrants multiplied and nativist groups formed independent political parties. In certain cities like Baltimore, New York, and Philadelphia, for example, anti-immigrant American Republican and Native American parties appeared in the 1830s and 1840s. They attracted working class and middle class voters angered by the job competition from immigrants, the increase in crime, public drunkenness, and pauperism that accompanied immigration, the supposed pollution of the body politic by ignorant immigrant voters, and an assertiveness by Catholic clergymen that supposedly threatened the nation's Protestant values and institutions.

By far the most massive and powerful political backlash against immigrants and Catholics before the Civil War, however, came with the Know Nothing movement of the mid-1850s. Not only did Know Nothings blame immigrants for economic, social, and political ills, but they focused on particular political actions by the Roman Catholic hierarchy, especially its attempt to secure public tax support for Catholic parochial schools, and the huge increase in the immigrant vote since 1848 as evidence that the long-warned of Papal plot to subvert America's republican institutions was reaching fruition. Demanding that immigrants be prevented from voting until they had resided in the United States for twenty-one years and that all foreigners and all Catholics be proscribed from public office, the Know Nothings, who began as another secret fraternity called the Order of the Star Spangled Banner, enlisted over a million members across the country in 1854 and 1855. In those years, moreover, their candidates won a string of astonishing political victories that smashed Lincoln's beloved Whig party while also contributing to massive Democratic defeats. During and after 1856, however, most northern Know Nothings were absorbed into the Republican party, and they would help elect Lincoln president in 1860, even though Lincoln himself had nothing but disdain for Know Nothings' anti-immigrant and anti-Catholic bigotry.