Preamble to the Articles of Confederation:
Whereas the Delegates of the United States of
America in Congress assembled did on the
fifteenth day of November in the Year of our
Lord One Thousand Seven Hundred and
Seventyseven, . . .
So, back to individual States with a quasi-nation in affect. The term United States of America was a term used for the Articles of Confederation, which remained until the Constitutional Convention in 1787 which re-designed the Articles of Confederation. That was the formal birth of the United States of America that the World accepted as a sovereign nation. Don't trust me?...Google.