The United States of America is the former country that is now replaced by the New United States.
The old United States was formed in 1788. At some point the Espheni arrived around Earth. After initial contact was unresponsive the Espheni attacked, unleashing an EMP and destroying the major cities around the world including New York, New York and Washington, D.C..(Live and Learn)
With the effect of the EMP disabling technology and the Espheni destroying the major cities, the United States government was unable to maintain control of the country and collapsed. Almost 2 years later, the Continental Congress is attempting to restore the former country to its previous state, its capital city was located in Charleston, South Carolina, which is now a ghetto.