US Constitution Series, Article VII

Article VII. RATIFICATION

The Ratification of the Conventions of nine States, shall be sufficient for the Establishment of this Constitution between the States so ratifying the same.

At the time of the original ratification, the Articles of Confederation were in effect. Those Articles required unanimous adoption by the states for an amendment. It seems odd that if they required unanimous approval for adoption that they could be replaced by 3/4 approval by the states (9 out of 13).

What would have happened to the state or states that refused to ratify? Would they be out of the union? Or would the ratifying states say that the non-ratifying states were abound anyway? Historically, all states ratified the constitution by conventions.