The venerable sage had the comfort of knowing that his words were not in vain.

Peace with Mexico was signed on February 2, 1848.
* * * * * Mr.Gallatin was no believer in the doctrine of 'manifest destiny,'-- the policy of bringing all North America into the occupation of a race speaking the same language, and under a single government.

On February 16, 1848, before news of the signature of the treaty at Guadalupe Hidalgo, by Mr.Trist, the American negotiator, was known in New York, Mr.Gallatin condemned this idea in a remarkable passage, in a letter to Garrett Davis:-- "What shall be said of the notion of an empire extending from the Atlantic to the Pacific and from the North Pole to the Equator?
Of the destiny of the Anglo-Saxon race, of its universal monarchy over the whole of North America?
Now, I will ask, which is the portion of the globe that has attained the highest degree of civilization and even of power--Asia, with its vast empires of Turkey, India, and China, or Europe divided into near twenty independent sovereignties?
Other powerful causes have undoubtedly largely contributed to that result; but this, the great division into ten or twelve distinct languages, must not be neglected.

But all these allegations of superiority of race and destiny neither require nor deserve any answer.

They are but pretences under which to disguise ambition, cupidity, or silly vanity." The justice of these reflections was assuredly borne out by the experience of history, but manifest destiny takes no account of past lessons.
Before these lines of Mr.Gallatin were penned, on January 19, 1848, gold was discovered in California.