This is a subject we touch on in the section on the Declaration of Independence which, if read literally, establishes the separate independence of each colony, not a unified group.
Historian Joseph Ellis builds upon this argument and challenges the idea that a national was really formed on July 4th, 1776. He recently published a book on that subject. He argues that the effort to develop the current constitution marks a "Second American Revolution" and is more properly considered the point when the United States of America became a nation.
Further, he argues that four key figures - George Washington, Alexander Hamilton, John Jay and James Madison - were responsible for this change. This helps put into context what was and was not accomplished by the Second Continental Congress in July 1776.
If you're interested:
- PBS NewsHour: A ‘quartet’ of patriots who brought the United States together.
- Boston Globe: ‘The Quartet’ by Joseph J. Ellis.
- Amazon: The Quartet: Orchestrating the Second American Revolution, 1783-1789.
- Wikipedia: Joseph Ellis.