Article 4, Section 3, Clause 1

Document 14

John Adams to Josiah Quincy

But I was about saying a word upon the Constitution. You appear to be fully convinced that the Convention had it not in contemplation to admit any State or States into our confederation, then situated without the limits of the thirteen States. In this point I am not so clear. The Constitution, it is true, must speak for itself, and be interpreted by [Volume 4, Page 549] its own phraseology; yet the history and state of things at the time may be consulted to elucidate the meaning of words, and determine the bonâ fide intention of the Convention. Suppose we should admit, for argument's sake, that no member of the Convention foresaw the purchase of Louisiana! It will not follow that many of them did not foresee the necessity of conquering, some time or other, the Floridas and New Orleans, and other territories on this side of the Mississippi. The state of things between this country and Spain in 1787, was such as to render the apprehensions of a war with that power by no means improbable. The boundaries were not settled, the navigation of the river was threatened, and Spain was known to be tampering, and England too.

The Founders' Constitution
Volume 4, Article 4, Section 3, Clause 1, Document 14
http://press-pubs.uchicago.edu/founders/documents/a4_3_1s14.html
The University of Chicago Press

The Works of John Adams. Edited by Charles Francis Adams. 10 vols. Boston: Little, Brown & Co., 1850--56. See also: Butterfield; Cappon; Warren-Adams Letters