As made clear by the first six words of the Constitution ("We the People of the United States"), the Constitution was created by and for the American people.
And that document had no validity or standing until it was ratified by the states. The American people were the citizens of the states, which were at that time members of the Articles of Confederation. By agreeing to the Constitution the states were in essence seceding from the Confederation. The difference being that no group of states was willing to use force to save a failing Confederation.