Final answer:
Plessy v. Ferguson upheld the "separate but equal" doctrine, but it was later overturned by the Brown v. Board of Education decision.
Step-by-step explanation:
Plessy v. Ferguson was a key Supreme Court decision that upheld the doctrine of "separate but equal." In this case, Homer Plessy, a man of mixed racial heritage, challenged a Louisiana law that required racial segregation on trains. The Supreme Court, in a 7-1 decision, ruled that the law did not violate the principle of equal protection under the law in the Fourteenth Amendment.
However, this decision was later overturned by the landmark case of Brown v. Board of Education in 1954. The Supreme Court, in a unanimous decision, declared that segregation in public schools was unconstitutional. This ruling overturned the "separate but equal" doctrine established in Plessy v. Ferguson and marked a significant milestone in the civil rights movement.
Thus, a key aspect of Plessy v. Ferguson was the affirmation of racial segregation as constitutionally acceptable, which was later invalidated by the Brown v. Board of Education decision.