Answer:
The Fourteenth Amendment to the Constitution of the United States was introduced after the Civil War. The clause, which was officially approved on July 9, 1868, includes articles that guarantee legal certainty and equal treatment: "No State will (...) deny any person within its jurisdiction the equal protection of the laws."
The amendment obliges all the states to treat every person within their territory as equals under the law. Also, every baby born on American territory was automatically granted American nationality.
When the amendment was adopted, these clauses were primarily intended to combat legalized racism, and to put an end to the issue of African American slavery and racial inequality in the United States.