The victory and territorial expansion Polk envisioned inspired patriotism among some sections of the United States, but the war and treaty drew fierce criticism for the casualties, monetary cost, and heavy-handedness.

[citation needed] Mexico's military and diplomatic capabilities declined after it attained independence from Spain in 1821 and left the northern half of the country vulnerable to attacks by Comanche, Apache, and Navajo Native Americans.

[21] The Comanche, in particular, took advantage of the weakness of the Mexican state to undertake large-scale raids hundreds of miles into the country to acquire livestock for their own use and to supply an expanding market in Texas and the U.S.[22] The northern area of Mexico was sparsely settled because of its challenging climate and topography.

[29] The British minister in Mexico, Richard Pakenham, wrote in 1841 to Lord Palmerston urging "to establish an English population in the magnificent Territory of Upper California", saying that "no part of the World offering greater natural advantages for the establishment of an English colony ... by all means desirable ... that California, once ceasing to belong to Mexico, should not fall into the hands of any power but England ... there is some reason to believe that daring and adventurous speculators in the United States have already turned their thoughts in this direction."

By the time the letter reached London, though, Sir Robert Peel's Tory government, with its Little England policy, had come to power and rejected the proposal as expensive and a potential source of conflict.

President Vicente Guerrero, a hero of Mexican independence, moved to gain more control over Texas and its influx of non-Hispanic colonists from the southern U.S. and discourage further immigration by abolishing slavery in Mexico.

[42]By the Treaties of Velasco made after Texans captured General Santa Ana after the Battle of San Jacinto, the southern border of Texas was placed at the "Rio Grande del Norte."

After telling both the Mexican governor and the American Consul Thomas O. Larkin that he was merely buying supplies on the way to Oregon, he instead went to the populated area of California and visited Santa Cruz and the Salinas Valley, explaining he had been looking for a seaside home for his mother.

General Antonio López de Santa Anna won those elections, but as was his practice, he left the administration to his vice president, who was again liberal Valentín Gómez Farías (December 23, 1846 – March 21, 1847).

The expression "Just like Gaines's army" came to refer to something useless, the phrase having originated when a group of untrained and unwilling Louisiana troops was rejected and sent back by General Taylor at the beginning of the war.

On April 25, 1846, a 2,000-man Mexican cavalry detachment attacked a 70-man U.S. patrol commanded by Captain Seth Thornton, which had been sent into the contested territory north of the Rio Grande and south of the Nueces River.

Unbeknownst to Farías, Santa Anna had secretly been dealing with U.S. representatives to discuss a sale of all contested territory to the U.S. at a reasonable price, on the condition that he be allowed back in Mexico through the U.S. naval blockades.

O'Sullivan, editor of the Democratic Review, coined this phrase in its context, stating that it must be "our manifest destiny to overspread the continent allotted by Providence for the free development of our yearly multiplying millions.

In the Senate on February 11, 1847, Whig leader Robert Toombs of Georgia declared: "This war is nondescript ... We charge the President with usurping the war-making power ... with seizing a country ... which had been for centuries, and was then in the possession of the Mexicans.

Prominent artists and writers opposed the war, including James Russell Lowell, whose works on the subject "The Present Crisis"[109] and the satirical The Biglow Papers were immediately popular.

He also elaborated upon the many outstanding financial claims by American citizens against Mexico and argued that, in view of the country's insolvency, the cession of some large portion of its northern territories was the only indemnity realistically available as compensation.

Walt Whitman enthusiastically endorsed the war in 1846 and showed his disdainful attitude toward Mexico and boosterism for Manifest Destiny: "What has miserable, inefficient Mexico—with her superstition, her burlesque upon freedom, her actual tyranny by the few over the many—what has she to do with the great mission of peopling the new world with a noble race?

The next day a large armed force of approximately 500 New Mexicans and Pueblo attacked and laid siege to Simeon Turley's mill in Arroyo Hondo, several miles outside of Taos.

The U.S. military moved quickly to quash the revolt; Colonel Price led more than 300 U.S. troops from Santa Fe to Taos, together with 65 volunteers, including a few New Mexicans, organized by Ceran St. Vrain, the business partner of William and Charles Bent.

[140] Commodore John D. Sloat, commander of the U.S. Navy's Pacific Squadron, near Mazatlan, Mexico, had received orders to seize San Francisco Bay and blockade California ports when he was positive that war had begun.

A Mexican campaign under Manuel Pineda Muñoz to retake the various captured ports resulted in several small clashes and two sieges in which the Pacific Squadron ships provided artillery support.

[174] American soldiers, including many West Point graduates, had never engaged in urban warfare before, and they marched straight down the open streets, where they were annihilated by Mexican defenders well-hidden in Monterrey's thick adobe homes.

On February 22, 1847, having heard of this weakness from the written orders found on an ambushed U.S. scout, Santa Anna seized the initiative and marched Mexico's entire army north to fight Taylor with 20,000 men, hoping to win a smashing victory before Scott could invade from the sea.

Furious fighting ensued, during which the U.S. troops were nearly routed, but managed to cling to their entrenched position, thanks to the Mississippi Rifles, a volunteer regiment led by Jefferson Davis, who formed them into a defensive V formation.

Northwestern Mexico was essentially tribal Native territory, but on November 21, 1846, the Bear Springs Treaty was signed, ending a large-scale insurrection by the Ute, Zuni, Moquis, and Navajo tribes.

Davis's concern was strategic and part of his vision of Manifest Destiny, considering that the Gulf of Mexico "a basin of water belonging to the United States" and that "the cape of Yucatan and the island of Cuba must be ours".

[194] Scott marched westward on April 2, 1847, toward Mexico City with 8,500 initially healthy troops, while Santa Anna set up a defensive position in a canyon around the main road and prepared fortifications.

"[219][220] The Treaty of Guadalupe Hidalgo, signed on February 2, 1848, by diplomat Nicholas Trist and Mexican plenipotentiary representatives Luis G. Cuevas, Bernardo Couto, and Miguel Atristain, ended the war.

This criticism, in which Congressman Abraham Lincoln played an important role with his Spot Resolutions, followed congressional scrutiny of the war's beginnings, including factual challenges to claims made by President Polk.

[267] The most infamous incident occurred on October 9, 1847, after Captain Samuel Hamilton Walker and 12 others were killed in a skirmish, Joseph Lane ordered his men to avenge the dead Texas Rangers by sacking the town of Huamantla.