Which amendment is known for defining U.S. citizenship?

The 14th Amendment is known for defining U.S. citizenship because it was enacted in 1868 in the aftermath of the Civil War, specifically to address the rights of former slaves. The amendment includes a crucial clause that states anyone born or naturalized in the United States is a citizen of the United States, which laid the foundation for citizenship rights. This amendment not only establishes citizenship but also ensures equal protection under the law and the due process of law for all citizens, which are fundamental aspects of American civil rights. By doing so, the 14th Amendment played a key role in shaping the legal and social landscape of citizenship in the U.S., making it a landmark piece of legislation in American history.