Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
United States (n.)
Usually our country’s name takes a singular verb: The United States is in a bad recession, and agreement requires as well a singular pronoun when the country is dealt with as a nation: It’s a great country. Occasionally we’ll hear or read about these United States, with plural verb and subsequent pronouns, but this is a conscious stylistic shift designed perhaps to stress the diversity of the country’s makeup, but more probably to embellish a flowery discourse. In all other circumstances, the United States [of America] is usually singular.
