What was the basis for the supreme court’s decision in plessy v. ferguson (1896) that upheld the constitutionality of a state law requiring segregated railroad facilities?

The basis of the Supreme Court's decision was the fact that the constitution does not prohibit segregation, it only mandates equal protection under the law. This was a supreme court case that the violated the 14th amendment; this was the the reason why Jim Crow laws were set up.