Final answer:
The major Supreme Court decision that established selective incorporation was Brown v. Board of Education.
Step-by-step explanation:
Selective incorporation, the process by which different protections in the Bill of Rights were incorporated into the Fourteenth Amendment guaranteeing citizens protection from state as well as national governments, was established in the major Supreme Court decision Brown v. Board of Education. This landmark case, decided in 1954, held that racial segregation in public schools was unconstitutional. The Court's ruling in this case extended the protection of the Fourteenth Amendment, specifically the Equal Protection Clause, to state laws and practices.