Where did the Founding Fathers come up with the term “natural-born citizen” that they used in the qualifications for President?

The term comes from The Law of Nations by Emerich de Vattel in 1758.

The Founders, all very learned and scholarly men, referenced many works as they deliberated on exactly what the Constitution should say: those of John Locke and Sir William Blackstone among them. But their ideas on citizenship obviously came from Vattel.

Benjamin Franklin ordered three copies of Vattel’s Le droit des gens (The Law of Nations) from the publishing house of Chez E. van Harrevelt in the original French. Upon receiving it, Franklin wrote to Vattel’s editor, C.G.F. Dumas, “I am much obliged by the kind present you have made us of your edition of Vattel. It came to us in good season, when the circumstances of a rising state make it necessary frequently to consult the Law of Nations. Accordingly, that copy which I kept has been continually in the hands of the members of our congress, now sitting, who are much pleased with your notes and preface, and have entertained a high and just esteem for their author.”

What exactly does Le droit des gens say about citizenship? In “§ 212 Of the citizens and naturals,” Vattel writes: “The citizens are the members of the civil society; bound to this society by certain duties, and subject to its authority, they equally participate in its advantages. The natives, or natural-born citizens, are those born in the country, of parents who are citizens. As the society cannot exist and perpetuate itself otherwise than by the children of the citizens, those children naturally follow the condition of their fathers, and succeed to all their rights. The society is supposed to desire this, in consequence of what it owes to its own preservation; and it is presumed, as matter of course, that each citizen, on entering into society, reserves to his children the right of becoming members of it. The country of the fathers is therefore that of the children; and these become true citizens merely by their tacit consent. We shall soon see whether, on their coming to the years of discretion, they may renounce their right, and what they owe to the society in which they were born. I say, that, in order to be of the country, it is necessary that a person be born of a father who is a citizen; for, if he is born there of a foreigner, it will be only the place of his birth, and not his country.”