This is one of the post-Civil War amendments to the US Constitution that includes the Due Process and Equal Protection Clauses.
Example: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
The excerpt above is part of the 14th amendment. This amendment was passed in 1868 and was supposed to help protect newly freed slaves. The goal in passing this was to ensure that African-Americans had the same legal rights as white citizens.
This due process clause has been used in several important Supreme Court cases to protect American citizens.
