Natural law?? go back to reading your comic books. Say something coherent for a change. That's a lie there in your second sentence. Madison clearly stated in the Federalist Papers, that states are superior to the Federal government, in those areas where they have not ceded power. A power not enumerated remains with the States as inviolably as if the US govt. did not even exist. Again your upside-downness is showing. You so want the Federal to be superior to the States, but nothing in our founding documents supports that desire.
You fail to realize that it's the Constitution, and not the Federal Government which is supreme over BOTH The Federal Govt. and the States. The Constitution reserves the rights of the States to form a voluntary Union, so in this respect the States are superior to the Federal Government, according to what Madison said. It's a voluntary Union.
You're right that States voulntarily jopined, but if a state can leave by a simple majority vote of its legislature then there was never any Union at all. I say that the Union was formed to protect my liberty, and if one State can break up the Union, then that one State can destroy my liberty since the protector of my liberty is threatened. No one state can ever take away my liberty.