“It’s the only definition of NBC we have. “
You have the Webster’s Dictionary. It is no harder than that. Look up the word ‘natural’. Vattel is not the law of the US and never was.
Webster’s Dictionary was first published in 1825, so would not have been of use to the Founders. Samuel Johnson published the first English language dictionary in 1750, but it was British. Yes, Cawdrey had his earlier Table Alphabeticall, but it was a listing of words without definitions.