Q. Does CMOS have a preference on the use of “America” as the country’s name versus the United States or US in formal writing? I know there is a distinction made for the abbreviation versus the spelled-out term, but I am curious if there is a preference on using “America” alone as the noun form of the country, not in reference to the people.
A. Though “America” is often used as shorthand for “the United States of America”—especially in speech—it’s usually better in formal writing to be more specific and use the first part of the name instead: “the United States” (or, to save space or avoid repetition, “the US”).
The adjective “American,” by contrast, is usually acceptable when referring to the United States (as in the phrase “American interests”), provided its meaning is clear from context. If “United-Statesian” weren’t so awkward (the link is to the entry in Merriam-Webster, which spells the adjective with a hyphen), then “American” might be less common than it is. If in doubt, use the adjective “US,” which is acceptable in even the most formal prose.
See also CMOS 10.37 (for “US” versus “United States”) and Garner’s Modern English Usage, 5th ed. (Oxford, 2022), under “American.”