[Cincinatus' Wife]

He writes:

I know states' rights advocates revere the 10th Amendment. But when the word "states" appears in the Constitution, it typically is part of a compound word, "United States," or refers to how the states and their people will be represented in the national government.

Before the Civil War it was, "These United States."

[ClearCase_guy]

Yes. Crucial distinction. We were once a federation of sovereign states. Lincoln turned us into a single government with state-level partitions.

[Lauren BaRecall]

An interesting history of the is/are debate:

http://www.visualthesaurus.com/cm/wordroutes/1907/