Many countries include ‘Democratic’ or ‘People’s’ in their names, even though they are not democratic and do not serve their people. Examples: Democratic People’s Republic of Korea Lao People’s Democratic Republic People’s Democratic Republic of Algeria Democratic Republic of the Congo And German Democratic Republic (East Side) in 1949–1990. None of these states are democratic, power and wealth are concentrated in the hands of a small ruling elite. Who are they fooling with these names?
if you stick strictly to the name “united states” then yes, it’s the first entity to name themselves this. later entities include the united states of belgium but they appear later (1790).
however, the netherlands used the name “united provinces” and “(republic of the seven) united netherlands” from 1588, sooooo I guess it can count if you make your question broad?
I wonder if the US founders knew about the Netherlands and thus tacked on “Of America”…somehow I doubt it