[vacri]

why isn't the USA the USNA

Even if you include the southern continent, there's no similar collection-of-states, so the USA is just as accurate as the USNA.

[pavlov]

There are actually two other large federal republics on the same continent. One is Estados Unidos Mexicanos, "United Mexican States", and the other is República Federativa do Brasil, "Federative Republic of Brazil".

[jmt7les]

Many people incorrectly refer to the entire country as just Mexico, which is actually just one state in the United States of Mexico.

[dllthomas]

Though to be fair, one of our states is not in either America.