The bottom of the page pls type Vattel in the search box provided. Vattel 1-9, the Dumas letter will appear.
http://www.franklinpapers.org/franklin/framedVolumes.jsp
If British Americans were not dutifully obligated to serve in the English military, then they were not in fact “natural born” English subjects, but subjects of a different class such as denizens aka inhabitants not afforded political status of full subjectship.