What group generally opposed both immigration and the influence of Catholicism in the US during the 1850s?

The Know Nothing Party emerged in the 1850s, primarily in response to the increasing numbers of immigrants, particularly those from Ireland and Germany, many of whom were Catholic. This party, also known as the American Party, was characterized by its nativist sentiments and sought to restrict immigration and limit the political power of Catholics, fearing that they would undermine American values and institutions. Their platform was built on anti-immigrant and anti-Catholic sentiments, which resonated with a portion of the American populace anxious about the changes brought by immigration.

The other groups listed had different focuses and were not primarily defined by nativist policies. Free-Soilers concentrated on opposing the expansion of slavery into the territories. The Whig Party was more centered on economic concerns and internal improvements, while the Democratic Party was more accommodating towards immigrants, including Catholics, as part of their broader political coalition. The Know Nothing Party’s specific opposition to both immigration and Catholic influence makes it the correct answer to the question.