The annexation of Texas, which in 1836 declared its independence from Mexico (with support from the U.S. government), paved the way for the war against Mexico. President James Polk, a Democrat and expansionist elected in 1844, confided to his secretary of the navy on the night of his inauguration in early 1845 that one of his main objectives as president was the acquisition of California, which was part of Mexico.
The Washington Union, a newspaper that represented the position of the Democratic Party, wrote: "Let the great measure of annexation be accomplished.... For who can arrest the torrents that will pour onward to the West? The road to California will be open to us." In the summer of 1845, John O'Sullivan, editor of the Democratic Review, used a phrase that would become famous, saying it was "Our manifest destiny to overspread the continent allotted by providence for the free development of our yearly multiplying millions." Yes, "manifest destiny."
All that was missing in the plan was an incident. A patrol of American troops was sent into territory between the Nueces River and the Rio Grande River that the Mexicans claimed was their land. The patrol was wiped out by Mexican forces. In response, Polk declared, falsely, that "Mexico... has invaded our territory and shed American blood upon the American soil."
Even before the incident, he had written in his diary that the United States had "ample cause for war." But Polk immediately asked Congress for a declaration of war. Congress rushed to approve, spending barely thirty minutes discussing the issue.
The Whig Party, which elected Abraham Lincoln to Congress in 1846, after the war had begun, was presumably against the war, but not against expansion. So they voted overwhelmingly for the war resolution. In Congress, Lincoln challenged Polk with his "spot resolutions," asking Polk to specify the exact spot where American blood was shed "on American soil." But, like the other Whigs, he would not try to end the war by stopping funds. The party voted again and again to appropriate the men and materials for the war.
There was resistance to the war by those Americans who saw expansion as a way of creating more slave territory. But that resistance broadened as the invasion of Mexico became a more and more bloody affair, accompanied by the bombardment of neighborhoods and the killing of women and children. The death toll of American soldiers grew. Volunteer regiments from Virginia, Mississippi, and North Carolina mutinied in northern Mexico against their officers. At least nine thousand soldiers deserted during the war.
Veterans returning home, desperate for money, sold to speculators the land warrants given by the government. The New York Commercial Advertiser pointed to the experience of the Revolutionary War, in which "immense fortunes were made out of the poor soldiers who shed their blood," and said the same thing was happening in the war against Mexico.
Mexico surrendered, and was paid $15 million by the U.S. government for the taking of New Mexico and California. A Whig newspaper concluded, "We take nothing by conquest.... Thank God."
In his diary1, Colonel Ethan Allen Hitchcock, in the 3rd Infantry Regiment, challenges, as an on-the-scene witness, the rhetoric of politicians who supported the war.From Voices of A People's History, edited by Zinn and Arnove
Fort Jessup, La., June 30, 1845. Orders came last evening by express from Washington City directing General [Zachary] Taylor to move without any delay to some point on the coast near the Sabine or elsewhere, and as soon as he shall hear of the acceptance by the Texas convention of the annexation resolutions of our Congress he is immediately to proceed with his whole command to the extreme western border of Texas and take up a position on the banks of or near the Rio Grande, and he is to expel any armed force of Mexicans who may cross that river. [William W. S.] Bliss read the orders to me last evening hastily at tattoo. I have scarcely slept a wink, thinking of the needful preparations. I am now noting [writing] at reveille by candlelight and waiting the signal for muster....Violence leads to violence, and if this movement of ours does not lead to others and bloodshed, I am much mistaken....
29th Aug. Received last evening... a letter from Captain Casey and a map of Texas from the Quarter-master-General's office, the latter being the one prepared by Lieutenant Emory; but it has added to it a distinct boundary mark to the Rio Grande. Our people ought to be damned for their impudent arrogance and domineering presumption! It is enough to make atheists of us all to see such wickedness in the world, whether punished or unpunished....
8th Sept.... General Taylor talks, whether sincerely or not, of going to the Rio Grande. This is singular language from one who originally and till very lately denounced annexation as both injudicious in policy and wicked in fact! The "claim," so-called, of the Texans to the Rio Grande, is without foundation. The argument of Mr. [Robert J.] Walker passes by the treaty of 1819, by which the United States gave up all west and south of the Sabine, either saying nothing about it or presuming that it was not valid. Yet we took possession of Florida under that treaty. The truth is that the limits of old Louisiana were never settled until by that treaty, so that the treaty of 1819 was really only a treaty of limits or boundary so far as Louisiana was concerned; and to say that the Senate, or treaty-making power, has no authority to determine a question of boundary, is preposterous. Louisiana had no fixed boundaries when Louis XV ceded it to Charles III of Spain and none when it was ceded back to France (to Napoleon), and continued to have none when it was purchased by the United States as much a foreign country as Yucatan, and we have no right whatever to go beyond the treaty.
As for Texas, her original limit was the Nueces and the hills ranging north from its sources, and she has never conquered, possessed, or exercised dominion west of the Nueces, except that a small smuggling company at this place, living here by Mexican sufferance, if not under Mexican protection, has chosen to call itself Texan, and some of the inhabitants have chosen to call themselves Texans....
C.C. [Corpus Christi], Sept. 20. ... He [Taylor] seems quite to have lost all respect for Mexicans' rights and willing to be an instrument of Mr. Polk for pushing our boundary as far west as possible. When I told him that, if he suggested a movement (which he told me he intended), Mr. Polk would seize upon it and throw the responsibility on him, he at once said he would take it, and added that if the President instructed him to use his discretion, he would ask no orders, but would go upon the Rio Grande as soon as he could get transportation. I think the General wants an additional brevet [medal], and would strain a point to get it....
2nd Nov. Newspapers all seem to indicate that Mexico will make no movement, and the government is magnanimously bent on taking advantage of it to insist upon "our claim" as far as the Rio Grande. I hold this to be monstrous and abominable. But now, I see, the United States of America, as a people, are undergoing changes in character, and the real status and principles for which our forefathers fought are fast being lost sight of. If I could by any decent means get a Irving in retirement, I would abandon a government which I think corrupted by both ambition and avarice to the last degree....
March 23rd. As to the right of this movement, I have said from the first that the United States are the aggressors. We have outraged the Mexican government and people by an arrogance and presumption that deserve to be punished. For ten years we have been encroaching on Mexico and insulting her.... Her people I consider a simple, well disposed, pastoral race, no way inclined to savage usages....
26th March.,.. We have not one particle of right to be here.
Our force is altogether too small for the accomplishment of its errand. It looks as if the government sent a small force on purpose to bring on a war, so as to have a pretext for taking California and as much of this country as it chooses; for, whatever becomes of this army, there it no doubt of a war between the United States and Mexico.
1 The Diary of Colonel Ethan Allen Hitchcock (June 30, 1845-March 26, 1846). In Ethan Allen Hitchcock, Fifty Years in Camp and Field: Diary of Major-General Ethan Allen Hitchcock, U.S.A., ed. W. A. Croffut (New York: G. P. Putnam's Sons/The Knickerbocker Press, 1909), pp. 192,198, 200, 203,212-13.