The political party known as know-nothing party gained influence because it focused on the people's concerns about

Immigration

Explanation:

The Know-Nothing party was a nativist party who were known for their resentment towards immigrants, like the Irish, and Catholicism. They would prevent Irish and other immigrants from being elected into political office and would also hope to deny these people jobs in the private sector, arguing that the nation's business owners needed to employ "true Americans".