The Know Nothings were extremely anti-immigrant and anti-Catholic. Many believed that Pope Pius IX, who was widely accused of being anti-democratic, had hatched a plot for millions of Catholics to immigrate into and then take over the U.S. by force of arms if not by ballots. Conspiracy theories ran rampant. The Know Nothing story was particularly popular among the American lower middle and skilled working classes, especially Protestants of English, Welsh, Scottish, Scotch-Irish, Dutch, and northern German ancestry. They saw the new immigrants as slovenly, stupid, criminal, and unwitting tools of unpatriotic Catholic bishops and corrupt city machine politicians. The Know Nothings argued that immigrants posed serious threats to traditional (their) American ways and therefore should be denied the rights to vote, run for public offices, and American citizenship when residency was less than 21 years.
The Know Nothings varied on points of emphasis in different parts of the country. In addition to anti-immigration and anti-Catholic sentiments, in some areas they were also anti-elitist and anti-intellectual. In other areas, they advocated social and political reforms that anticipated future popular causes, especially temperance and Progressive political reforms.
The Native American Party (with “Native” meaning white and older generational Americans, not Indians) swept elections in Massachusetts in 1854. The Know Nothings also exercised major political strength in Pennsylvania, Ohio, Indiana, Illinois, Maryland, and California (where the anti-immigration hatred was directed at the Chinese). They successfully elected mayors in Boston, Philadelphia, Chicago, and San Francisco. The movement hit a high point of popularity in 1855, and then began to decline after a serious Know Nothing riot killed 22 people and wounded many others in Louisville. The American Party ran candidates for President and Vice President in 1856, but then virtually disappeared by 1860.
It was another issue that eclipsed the anti-immigration movement: slavery. Northern Know Nothings migrated to the Republican Party, even though Abraham Lincoln of Illinois disapproved of them. (The Irish and German immigrants, by the way, became furiously loyal to the Union and supplied numerous troops for Lincoln's army.) In the South, the Know Nothings bitterly opposed Lincoln and supported secession when racial proved stronger than ethnic prejudice.
Periodically, nativist groups have gained popularity in American politics because they reflected deep fears and biases concerning generation-after-generation of newcomers to the U.S. Once each immigrant group took hold in America, they tended to object to new immigrant groups, which were seen as threats on several levels. Having worked so hard to win social respect and middle-class lifestyles, Americans have jealously guarded their advantages against foreign-born intruders. There have always been Know Nothings. They may even exist today.