The Polk administration was one of achievement -- the president had success in every major initiative he undertook in four years -- but the signal achievement of his presidency literally changed the map of the United States. The war with Mexico might have been, as US Grant observed in his Memoirs, "an instance of a republic following the bad example of European monarchies, in not considering justice in their desire to acquire additional territory," and most modern historians would probably agree with that assessment. But no one is suggesting the return of the territory thus won, about 529,000 square miles, to Mexico. Polk's legacy stands.
On February 2, 1848, US and Mexican negotiators inked the Treaty of Guadalupe Hidalgo just north of Mexico City. The US representative was Nicholas Trist, "a colorful and eccentric figure... who had studied law with Jefferson and been private secretary to Jackson," wrote Page Smith in The Nation Comes of Age (1981). "Trist knew Spanish and... was handsome and urbane but conceited and self-important."
Trist had been send by President Polk to conclude a treaty, but before long the president had second thoughts, and recalled him. It wasn't merely a matter of picking up a telephone, however, as a modern president can do. Trist ignored his recall and pressed on.
"Although Trist had been ordered home by Polk," Page continued, "who had denounced him as 'impudent, arrogant, very insulting, and personally offensive,' he remained with [General Winfield] Scott and pushed negotiations for peace... When Polk received a copy of the treaty, he was at first disposed to reject it, but a majority in Congress pressed him to send it to the Senate for ratification and it passed that body by a vote of 38 to 14."
Grant had this to say about the treaty many years later: "It is to the credit of the American nation, however, that after conquering Mexico, and while practically holding the country in our possession, so that we could have retained the whole of it, or made any terms we chose, we paid a round sum for the additional territory taken; more than it was worth, or was likely to be, to Mexico. To us it was an empire, and of incalculable value; but it might have been obtained by other means."