The "separate but equal" principle declared that as long as public facilities were equal in quality, segregation of white and black individuals did not violate the Equal Protection Clause that had been included in the 14th Amendment to the US Constitution (Reconstruction Amendment). This clause guarateed equality of rights for all US citizens, without discrimination in terms of race, color or prevision condition of servitude.
The landmark decision adopted in Plessy v. Ferguson in 1896, accepted the "separate but equal" principle and enabled segregation to proliferate under the constitutional framework.