So no "The USA are", as much sense as that makes.
"The USA is" is accepted. In English, the USA/United States/U.S.A/United States of America/etc. is a single county so even though "states" is plural, it takes a singular verb.
the united states is a country of immigrants should also be accepted, wth?! it's not a mistake, i'm reporting it unless im told it's wrong!
That answer is already among the accepted translations. Please ensure there are no typos before reporting. I received this report: the united stated is a country of immigrants.