How easily we forget that the Declaration of Independence only predicted the USA in retrospect. The Declaration was the military and political alliance of 13 colonies, each of which was self-governing within the generous limits established by Britain. In the Declaration they proclaimed themselves to each be a "state," ie a nation, independent from Britain, and to join to remove British colonial control, by force of arms if necessary.
Each state coveted its autonomy, during and after the war. There was no US until 1789 when those independent 13 states, after much dithering, politicking, and ambivalence, agreed to cede some small amount of power, besides the power to run the Continental Army, to a united Federal government.
They were all, naturally, and rightly, suspicious about the idea. But the State of New York, as I understand it, gets the main credit for insisting on the addition of a Bill of Rights before being willing to sign on to the document. Many delegates felt that enumerating all of those rights - and more - was unnecessary and obvious.
Image: Weisgerger's painting of Betsy Ross presenting the flag of the Continental Army in 1777 - what was called the flag of the "Grand Union." Prior to that time, the Army had only State and militia flags and banners.