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.

the treaty of brest-litovsk was a peace treaty signed on 3 march 1918 between the new bolshevik government of russia and the central powers (german empire, austria-hungary, bulgaria, and the ottoman empire), that ended russia's participation in world war i.