If that were true the United States would be referred to in the singular.
Your interpretation ignores the first phrase, Kevin. The term being defined is treason against the entity known as the United States.
My interpretation doesn't ignore it at all. My interpretation simply acknowledges that the phrase "United States" is qualified by being referred to in the plural rather than the singular.
Hardly qualified, but an affectation of late 18th and early 19th Century formal writing when referring to the Federal entity. That aside, treason can only be committed against the sovereign. Are you arguing that the Federal constitution outlining and controlling the Federal government applies only to the individual States, and does not create a new, sovereign entity?