Huh? We were a country after July 4, 1776. We became the United States of America on that date.
the constitution was adopted 6/21/1788.
The US Constitution was our third governing document. The Articles of Confederation came before it in 1781,
and of course the Declaration was the document that founded the new nation.
What am I missing ?
I think you are conflating the writing of the US Constitution with the founding of the United States. This is incorrect. The United States was created by the Declaration of Independence. The Constitution was just a governing charter.
It didn't even go into effect until June 21, 1788. By this time, we had been an independent nation for 12 years.