The legal doctrine that upheld the practice of racial segregation in the U.S. is known as **"separate but equal,"** established by the Supreme Court case Plessy v. Ferguson in 1896. This decision affirmed the constitutionality of racial segregation laws, allowing states to maintain separate facilities for race groups as long as they were purportedly equal. The doctrine legitimized systemic racism and reinforced discriminatory practices, particularly in public accommodations, schools, and transportation. It wasn't until the landmark Brown v. Board of Education decision in 1954 that the Supreme Court ruled that segregated schools were inherently unequal, leading to the doctrine's eventual demise.