Final answer:
The Know-Nothing movement or American Party was the name given to the anti-immigrant anti-Catholic sentiments that spread in the 1800s. This movement was fueled by Protestant Americans' fear and distrust of Catholic immigrants, particularly Irish Catholics.
Step-by-step explanation:
The anti-immigrant anti-Catholic sentiments that spread in the 1800s were known as the Know-Nothing movement or American Party. This movement, also referred to as nativism, was fueled by Protestant Americans' fear and distrust of Catholic immigrants, particularly Irish Catholics. The Know-Nothing Party gained popularity by opposing further immigration and promoting legislation to restrict the entry of Irish and other Catholic immigrants into the United States.