Which political party was founded as a single-issue party in opposition to Freemasonry?

The Anti-Masonic Party was founded in the early 1830s as a response to rising public concern about the influence and secrecy of the Freemasons in American politics and society. It emerged during a time when the public was becoming increasingly aware of the perceived elitism and lack of transparency associated with secret societies. The party capitalized on the widespread unease that came from incidents such as the disappearance of William Morgan, who was believed to have been kidnapped and possibly killed for attempting to expose Freemasonry's secrets.

As a single-issue party, the Anti-Masonic Party focused primarily on opposing Freemasonry and advocating for anti-Masonic sentiments. This focus allowed them to attract a following among various demographic groups who felt that secret societies had undue influence over politics and governance. Their platform also touched on broader themes of political reform and accountability, but the central tenet was their staunch opposition to Freemasonry.

This historical significance makes the Anti-Masonic Party the correct choice, as it represents the early emergence of party politics in the United States, particularly in how it addressed specific societal concerns of the time.