What amendment made all persons born or naturalized in the U.S. citizens?

The 14th Amendment is significant because it explicitly states that all persons born or naturalized in the United States are citizens. This amendment was adopted in 1868, primarily to secure rights for formerly enslaved individuals following the Civil War. The inclusion of the citizenship clause was pivotal in establishing a legal framework that upholds the principle of equality under the law and ensures that citizenship cannot be denied based on race, color, or previous condition of servitude.

This amendment also includes the Equal Protection Clause, which has been foundational in furthering civil rights and protections in the United States. Understanding the 14th Amendment is key to grasping the evolution of citizenship and civil rights in American history, making it a critical aspect of the legal landscape today.