Which Supreme Court case established the superiority of federal law over State law?

There was no case necessary, the Supremacy Clause of the Constitution states that the ';Constitution and the laws of the United States...shall be the supreme law of the land...anything in the constitutions or laws of any State to the contrary notwithstanding.'; This means of course, that any federal law--even a regulation of a federal agency--trumps any conflicting state law.





There have been several cases interpreting preemption doctrine (invalidating state law based upon closely related Federal Laws), Pennsylvania v Nelson (1956), Cipollone v Liggett Group (1992) and most recently Gonzales v Oregon (2006) where the court found that the Fed. Controlled Substances Act did not preempt the state of Oregon from allowing doctors to prescribe lethal doses of drugs (i.e. assisted suicide).





Hope this helps.Which Supreme Court case established the superiority of federal law over State law?
Actually, I believe the Supremacy Clause of the Constitution is the source for the supremecy of federal law over state law in certain areas:





Article VI, Clause 2 of the United States Constitution





';This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the authority of the United States, shall be the supreme Law of the land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.';





McCulloch v. Maryland and Gibbons v. Ogden are two of the earliest cases which interpreted the Supremacy Clause.