The Anti-Federalists were a group of individuals in the late 18th century who opposed the ratification of the U.S. Constitution. They believed that the new government would create a central authority that was too powerful and could threaten individual liberties and state sovereignty. Prominent figures among the Anti-Federalists included Patrick Henry and George Mason, who argued for a Bill of Rights to protect citizens' freedoms. Anti-Federalists were concerned that the Constitution lacked specific protections for individual rights and favored a more decentralized government structure. Their opposition led to the eventual adoption of the Bill of Rights in 1791, which addressed many of their concerns by guaranteeing fundamental rights such as freedom of speech and religion.