Final answer:
The Fourteenth Amendment to the United States Constitution was used to justify segregation, as interpreted by the Supreme Court in the case of Plessy v. Ferguson. However, the Brown v. Board of Education case in 1954 reversed this ruling and deemed segregation in public schools unconstitutional.
Step-by-step explanation:
The amendment that was used to justify segregation in the United States was the Fourteenth Amendment. Although the Fourteenth Amendment was intended to protect the rights of African Americans and provide equal protection under the law, the Supreme Court interpreted it to be consistent with segregation. The landmark case of Plessy v. Ferguson in 1896 affirmed that segregation was constitutional as long as the separate facilities were considered 'equal.'
However, in 1954, the Supreme Court case of Brown v. Board of Education overturned the Plessy v. Ferguson ruling, declaring that segregation in public schools was unconstitutional. This decision marked a significant milestone in the fight against segregation and paved the way for future legal actions to dismantle segregation in various institutions.