"The United States of America (is/are) ...", where in US English "is" is the correct version. Interesting, I didn't know that. I'd have presumed that one would

"The United States of America (is/are) ...", where in US English "is" is the correct version. Interesting, I didn't know that. I'd have presumed that one would use "is" when referring to the country, and "are" when referring to the group of states. Is this incorrect? (for what it's worth, I'm from the UK ;)