The significance of the 14th Amendment to the U.S. Constitution lies in its establishment of citizenship and equal protection under the law. Ratified in 1868, it granted citizenship to all persons born or naturalized in the United States, which included former slaves following the Civil War. The amendment also aimed to ensure that states could not deny any person the equal protection of the laws, effectively laying the groundwork for future civil rights movements. Its provisions have been pivotal in numerous Supreme Court cases and have played a crucial role in advancing social justice and civil liberties in America.