The American Party (also called the Know Nothing Party, American Republican Party, and Native American Party) was the chief product of the Know Nothing movement. The movement began in the 1840s and remained fairly popular through the 1850s. It primarily gave voice to nativist opposition to the increasing immigration of Irish Catholics and other non-Anglo Saxon Protestants into the United States. The American Party represented the political wing of the movement and was founded in New York City in 1843. The party enjoyed some initial success (winning the 1844 New York mayoral election) but became a substantial political force in the 1850s as disaffected Whigs joined its ranks. Those who joined tended to be Whigs that supported the Compromise of 1850 and thus injected a new Unionist element to the party's platform. Party members selected Millard Fillmore as their presidential candidate in 1856 but he placed a distant third behind Democrat James Buchanan and Republican John C. Fremont. The defeat and subsequent viability of the Republican Party permanently crippled the American Party and the Know Nothing movement, which largely dissolved by the 1860s.
Tyler Anbinder, Nativism and Slavery: The Northern Know Nothings and the Politics of the 1850s (Oxford: Oxford University Press, 1992); Michael F. Holt, Political Parties and American Political Development: From the Age of Jackson to the Age of Lincoln (Baton Rouge: Louisiana State University Press, 1992); Jean H. Baker, Ambivalent Americans: The Know-Nothing Party in Maryland (Baltimore: Johns Hopkins University Press, 1977); W. Darrell Overdyke, The Know-Nothing Party in the South (Baton Rouge: Louisiana State University Press, 1950); Ray A. Billington, The Protestant Crusade, 1800-1860: A Study of the Origins of American Nativism (New York: Macmillan, 1938).