Why did the phrase separate but equal become associated with the Supreme Court ruling against Homer Plessy (Plessy v. Ferguson 1896)?

Plessy v. Ferguson was a landmark 1896 U.S. Supreme Court decision that upheld the constitutionality of racial segregation under the “separate but equal” doctrine. As a result, restrictive Jim Crow legislation and separate public accommodations based on race became commonplace.

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