Which decision is indicative of how the Supreme Court interpreted the Fourteenth Amendment and state discretion in civil rights matters in the decades after the Civil War?

Plessy v. Ferguson

Explanation:

Plessy v. Ferguson was a landmark ruling of the United States Supreme Court  in 1896 that provided legal justification for segregation and upheld the constitutionality of racial segregation laws on buses, public facilities etc.

This case came as a result of an incident in which an African American train passeger Homer Plessy refused to sit in the black only section of the train. Plessy argue that segregation law violate the Equal Proctection Clause of th Fourteenth Amendment which forbids states from denying any person within their jurisdiction the equal protection of the laws. However Ferguson ruled that separate but equal facilities were constitutional.

Ferguson stand came to be known as separate but equal doctrine

Supreme Court Of The United States. U.S. Reports: Plessy v. Ferguson, 163 U.S. 537 . 1895.