The pertinent sentence of the Constitution reads:
"To define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations;"
Piracies and Felonies are clearly separate items. They are single words. They are nouns.
It then goes on to state "Offences" against something.
Against what?
Against the Law? The Law of What? Just the Law? Who's Law?
Clearly...
the "Law of Nations"
"Law of Nations" is NOT a noun. What it appears to be, as stated by WILLIAM R. NIFONG from the Duke Law Journal article above, is a reference to a collection of ideas found in a particular Book Title.
Furthermore, "Law of Nations" is contained in a sentence that deals with what?
It deals with "Piracies" and "Felonies committed on the high Seas"
That sounds VERY familiar if one is familiar with Vattel's "Law of Nations."
I believe that your theory that the phrase "Law of Nations" is merely a noun, is unfounded.
The phrase "law of nations" was the 18th century term for what we today call "international law." The Supreme Court uses the phrase in that sense many times in the 18th and 19th centuries. Vattel wrote a book about international law. The Constitution gave Congress the power to criminalize acts in violation of international law (e.g., war crimes). The words "Law" and "Nations" are capitalized not because they refer specifically to Vattel's book, but because all nouns in the Constitution were capitalized. Unless you are saying that "Piracies and Felonies" is also the name of a book? How about "high Seas"-- why is "Seas" capitalized?
Once you recognize that all nouns in the Constitution are capitalized, the theory that "Law of Nations" refers specifically to Vattel's book, as opposed to being a general reference to a topic which Vattel happened to write about, falls apart.