As Eugene Volokh explains here, the grammatical shift from "the United States are" to "the United States is" has often been attributed to a change in national identity following the Civil War. In other words, the singular verb became dominant as a result of the political recognition that the U.S. constitutes a single, indivisible country, rather than a federation of inherently separate states. Eugene points out, however, that the actual linguistic change occurred over a period of many years, and not immediately following the Civil War. Quoting Minor Myers in The Green Bag, he notes that SCOTUS "continued to use the plural form through the end of the nineteenth century. Indeed, the plural usage was the predominant usage in the 1870s, 1880s, and 1890s. Only in the beginning of the twentieth century did the singular usage achieve preeminence and the plural usage disappear almost entirely."
SCOTUS usages, of course, are not definitive, but Myers's observation does make me wonder about the supposed political implications of the verb change. As Shelby Foote put it (and quoted by Mark Liberman of Language Log), after the Civil War "it was always 'the United States is,' as we say today without being self-conscious at all. And that sums up what the war accomplished. It made us an "is."
Perhaps there is a simpler, non-political explanation. In British English, collective nouns have always taken plural verbs. Thus, a Brit would say, for example, "the faculty are meeting" and "the team are practicing." This currently sounds odd to American ears, as we use singular verbs with collective nouns: "Congress is in session" and "the orchestra is playing."
American and British English have diverged over time, and usages must have been much closer in 1787 than they are today. When the Constitution was written, it seems evident that collective nouns were regarded as plural on both sides of the Atlantic. Thus, Article Three provides that "Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies." That was not a reflection on the nature of government, however; rather, it was simply the standard grammar of the time.
But just as American spelling is no longer the same as it was in 1787, so have our rules changed regarding subject-verb agreement.
Although there appears to have been an inflection point in the 1860s, that is probably an example of the salience error or the coherence fallacy. We tend to notice the change around that time because we are looking for it. And likewise, we tend to believe that events occur for reasons, rather than randomly. As a dominant event in U.S. history, the Civil War provides a persuasive explanation for a linguistic switch, when in fact, as Myers demonstrated, it was actually a much longer and slower process.
In that analysis, there is no political valence whatsoever to the subject-verb shift, which is simply an artifact of linguistic change over time. This is all supposition on my part -- and I am certainly no expert -- but I think it has a lot of explanatory power.
UPDATE: According to Google Ngram, "the United States is" became preponderant in the late 1830s, well before the Civil War, and peaked in the 1920s-1940s. Interestingly, "the United States are" still accounts for almost one third of references after 2000.
The Google n-gram data are worth a look.
Posted by: Joe Miller | January 18, 2018 at 09:15 AM
https://books.google.com/ngrams/interactive_chart?content=the+united+states+is%2C+the+united+states+are&case_insensitive=on&year_start=1708&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t4%3B%2Cthe%20united%20states%20is%3B%2Cc0%3B%2Cs0%3B%3Bthe%20United%20States%20is%3B%2Cc0%3B%3BThe%20United%20States%20is%3B%2Cc0%3B.t4%3B%2Cthe%20united%20states%20are%3B%2Cc0%3B%2Cs0%3B%3Bthe%20United%20States%20are%3B%2Cc0%3B%3BThe%20United%20States%20are%3B%2Cc0
Posted by: Joe Miller | January 18, 2018 at 09:23 AM
Interestingly, though treated as a singular noun for proper verb usage, "United States" is treated as a plural for possessive purposes. Thus, you don't ever add an "s" after a possessive apostrophe (like you would for, say, "Arkansas"). http://grammarist.com/usage/united-states/
Someone call Bryan Garner!
Posted by: Scott Dodson | January 18, 2018 at 12:07 PM
Speaking of "linguistic" change over time, since January 20, 2017, 12:01 pm we are either in Amurica or Murika. MAGA
Posted by: Deep State Special Legal Counsel | January 18, 2018 at 01:35 PM