The 14th Amendment, passed after the Civil War, changed the relationship between citizens and their state governments. It contains some of the most important words in the Constitution, including the "Equal Protection Clause."
The amendment guarantees that anyone born in the United States is a U.S. citizen, regardless of who their parents are or where they came from.
It prohibits states from taking away a person's life, liberty, or property without "due process of law"—ensuring that states must follow fair procedures before punishing anyone.
The most famous part says that no state can "deny to any person... the equal protection of the laws." This has been used to strike down laws that discriminated based on race, gender, and other personal characteristics.