Skankbeat has re-discovered a grammatical change noted by the historian Shelby Foote.
Shelby Foote in Ken Burns's The Civil WarBefore the war, it was said "the United States are." Grammatically, it was spoken that way and thought of as a collection of independent states. And after the war, it was always "the United States is," as we say to day without being self-conscious at all. And that's sums up what the war accomplished. It made us an "is."
Foote did not see the legal ramifications of that change, but then he was not a legal scholar on a par with Skankbeat.