What was the Know-Nothing party of the 1850s?

The Know Nothing movement was a American political movement of the 1840s and 1850s. It was empowered by popular fears that the country was being overwhelmed by Irish Catholic immigrants, who were often regarded as hostile to U.S. values and controlled by the Pope in Rome. Mainly active from 1854 to 1856, it strove to curb Immigration and naturalization, though its efforts were met with little success. There were few prominent leaders, and the largely middle-class and entirely Protestant membership fragmented over the issue of slavery. Most ended up joining the Republican Party by the time of the 1860 presidential election.