Which amendment defines a U.S. citizen as anyone born or naturalized in the United States?

The Fourteenth Amendment is the correct choice because it specifically addresses citizenship in the United States. Ratified in 1868, this amendment contains the Citizenship Clause, which states that all persons born or naturalized in the U.S. are citizens of the country. This was a significant development in American law, particularly following the Civil War, as it ensured that former slaves and their descendants were granted full citizenship rights.

The other amendments listed do not focus on defining citizenship. The First Amendment primarily protects freedoms related to religion, speech, press, assembly, and petition. The Fifth Amendment deals with legal rights including due process and protection against self-incrimination. The Ninth Amendment addresses the rights of the people that are not specifically enumerated in the Constitution. Thus, the Fourteenth Amendment is uniquely positioned as defining U.S. citizenship and protecting the rights of individuals in that capacity.