Final answer:
The Supreme Court's decision in Plessy v. Ferguson established the 'separate but equal' doctrine, legitimizing racial segregation as constitutional if facilities for both races were equal.
Step-by-step explanation:
In the landmark decision of Plessy v. Ferguson in 1896, the Supreme Court ruled that racial segregation was constitutional as long as the facilities provided for both races were equal, a doctrine known as 'separate but equal.' The Court's decision legitimized state laws establishing racial segregation and upheld the legality of separating the races in public accommodations, such as railroads, as per the Fourteenth Amendment's equal protection clause. This ruling reinforced the institutionalized system of racial discrimination, later known as the Jim Crow laws, creating a precedent that permitted segregation for more than half a century until it was finally overturned by the Brown v. Board of Education decision in 1954.