One of the reasons nativists opposed immigration is because they felt that immigrants were willing to work for any wage, which would make it harder for native-born American citizens to find jobs. The nativist movement in the U.S. began in the early 1800s with clashes between nativists and immigrants turning violent by the 1830s.
Anti-Catholic sentiments led to riots in some American cities as nativist Protestants clashed with Irish-Catholic immigrants. Some of these confrontations were sparked by the differences between Protestantism and Catholicism and the nativist fear of Romanism and Catholics' loyalty to the Pope. Some of the most extreme violence occurred during the Kensington Riots of 1844 in Philadelphia, during which troops were called in to put down armed clashes between nativist Protestants and Catholics.
The nativist movement was also an attempt to gain political power by capitalizing on xenophobia. The movement went public and formed the American Party in 1854 and unsuccessfully ran former president Millard Fillmore as a party candidate in the 1856 presidential race.
Anti-German nativist sentiments led to a suppression of German culture beginning in the 1840s and leading up to 1920. Chinese immigrants began being targeted in the 1870s and nativists started focusing on Jews and south-eastern European immigrants in the years following World War I. By this time, the nativist movement had become linked to the eugenics movement and the concept of preserving racial purity. Opposition to immigrants from Italy and Poland flooding the labor market began in the 1920s, and it has now become focused on immigrants from Mexico and Central America.