The Know Nothing Party was a political movement in the United States during the mid-19th century, primarily active in the 1850s. It emerged in response to the increasing number of immigrants, particularly from Ireland and Germany, and was characterized by its nativist sentiments. Members believed that American society should be preserved for native-born citizens and often opposed immigration and the influence of Catholicism. The party's name originated from its secretive nature; members would respond "I know nothing" when asked about their activities. Although it gained significant popularity and even won some elections, the Know Nothing Party eventually declined as internal divisions and the rising tensions over slavery overshadowed its agenda.