On September 9, 1776, the Second Continental Congress adopted a new name for what had been called “the United Colonies.” The moniker United States of America has remained since then as a symbol of freedom and independence.
Benjamin Franklin popularized the concept of a political union in his famous "Join, Or Die" cartoon in 1754. A generation later, the concept of unity became a reality. Thomas Jefferson is credited as being the first person to come up with the name, as he was drafting the Declaration of Independence. In June 1776, Jefferson’s draft version of the Declaration started with the following sentence: “A Declaration of the Representatives of the UNITED STATES OF AMERICA, in General Congress assembled.” The final version of the Declaration starts with the date July 4, 1776 and the following statement: “The unanimous Declaration of the thirteen united States of America.”
Richard Henry Lee of Virginia had used the name “United Colonies” in a June resolution to Congress: "Resolved, That these United Colonies are, and of right ought to be, free and independent States, that they are absolved from all allegiance to the British Crown, and that all political connection between them and the State of Great Britain is, and ought to be, totally dissolved,” Lee wrote.
These thoughts are included in the Declaration’s final paragraph. “We, therefore, the Representatives of the united States of America, in General Congress, Assembled, appealing to the Supreme Judge of the world for the rectitude of our intentions, do, in the Name, and by Authority of the good People of these Colonies, solemnly publish and declare, That these United Colonies are, and of Right ought to be Free and Independent States,” it reads.
On Monday, September 9, 1776, the Congress moved to approve some important resolutions, including payments for the army. The fifth resolution read as follows: “That in all continental commissions, and other instruments, where, heretofore, the words ‘United Colonies’ have been used, the stile be altered for the future to the “United States.”
John C. Fitzpatrick from the Library of Congress, back in 1920, explained the origin of “United Colonies” and the abbreviation “U.S.A.” in an article for the Daughters of the American Revolution magazine.
Fitzpatrick said the words United Colonies were used by the Congress when it appointed George Washington as commander in chief in June 1775. The abbreviation U.S.A. had its origins as a way that government inspectors approved official gunpowder. Fitzpatrick said the army needed to have inspectors verify that gunpowder met standards, and it stamped “U.S.A.” on the casks as a mark, starting in August 1776,
Also, the words “United States of America” appeared in the first draft of the Articles of Confederation on July 8, 1776, as it was submitted to Congress. The Articles weren’t ratified by the states until March 1781.