[citation needed] U.S. president James K. Polk had decided that an invasion into central Mexico via the Gulf Coast port of Veracruz would make the Mexicans come to the negotiating table.

Worth's 1,000 men advanced onto undefended Saltillo on November 16, despite orders to halt any movement further south, considering it strategic to cover the approaches to Monterrey and Parras de la Fuente.

In mid-August 1846, General Antonio López de Santa Anna returned from exile and quickly assumed command of the Mexican Army, having tricked Polk into allowing him to return to Mexico, telling him that he could reconcile Mexico to make peace with the U.S.[5][1]: 202  He reached San Luis Potosí on October 8 with a force of 20,000 men and 5,000 women (soldaderas).

[1]: 202  General José de Urrea's cavalry would simultaneously retake Ciudad Victoria and cut off Monterrey from the port of Matamoros, Tamaulipas.

[1]: 202  Santa Anna's army departed San Luis Potosí on January 27 with a force of 21,553, and reached Encarnación, south of Saltillo, with 15,142 men on February 20.

The men and women in Santa Anna's forces began to die of exposure, and thirst once the cold weather lifted was also a problem.

Some soldaderas set fire to trees around the encamped troops to warm them, but by the time the two armies fought, the Mexican forces had already lost thousands to illness, exposure, and desertion.

[11] Taylor moved 4,650 of his men to Agua Nueva on February 14, but on February 20, Major Benjamin McCulloch's Texas Rangers encountered Santa Anna's force at Encarnación, prompting Taylor's withdrawal to La Angostura ("the narrow place"), a mile and a quarter south of Hacienda San Juan de la Buena Vista.

[1]: 209  General Wool was charged with selecting "the field of battle" and making "such dispositions of the troops on the arrival of the enemy" as he deemed necessary.

[1]: 210  Continuing to the left was the 2nd Illinois under Colonel William H. Bissell, General Joseph Lane's Indiana Brigade, and the Kentucky and Arkansas horsemen, with two squadrons of dragoons and a company of Texans in reserve.

[1]: 211 Santa Anna had chosen the day of battle, not apparently aware that it was George Washington's birthday, which galvanized patriotic sentiment among the U.S. forces.

A captured U.S. soldier said the Mexicans found it hard to believe that General Washington had not been leading the troops himself, but had been dead for nearly fifty years.

[1]: 211  During the night, Brigadier General Manuel Micheltorena moved five 8-pounders above the American left, intending to flank them along the high ground the next morning at daylight.

[1]: 212  The 2nd Indiana faced a force of 7,000 Mexicans, prompting Wool to send the 2nd Illinois and Captain Thomas W. Sherman's battery in support.

[1]: 212 The Hoosiers, after taking 90 casualties, broke and fled, forcing the 2nd Illinois into a slow fighting withdrawal, and Marshall's men to flee northward to the Buena Vista hacienda.

[1]: 214 Davis' Mississippians were ordered to shield Buena Vista along with the volunteers of the Arkansas and Kentucky cavalry, the 3rd Indiana, and Captain Enoch Steen's dragoons.

[1]: 214  A large Mexican force routed the cavalry, killing Archibald Yell, and then reached the hacienda of Buena Vista.

They had expected the building to be full of provisions, but instead they were dismayed to find that U.S. troops taking refuge in it were persuaded by their officers to defend it.

[1]: 216  Later, this order, although misquoted as "give them a little more grape, Captain Bragg", would be used as a campaign slogan that carried Taylor into the White House.

[15] On February 23, some of Santa Anna's council of war at Agua Nueva advised withdrawal,[1]: 217  while others argued that cattle could be driven there to provision the soldiers.

Santa Anna's forces had captured important war trophies from the U.S. Army, cannons and flags, as well as arms, which remained on display into the modern era at the Artillery School of Mexico.

[18] In the account written by Mexicans in the immediate aftermath of the 1848 Treaty of Guadalupe Hidalgo ending the war, they considered the battle a victory.

[22] Also killed were Archibald Yell, former governor of Arkansas,[23] and John J. Hardin of Illinois, a Whig political rival of Abraham Lincoln.

[27] Since the American forces were largely volunteers rather than regular army, it increased Buena Vista's popularity in the public imagination.

"There the wrecks lay in awful significance--dead men and horses, bayonets, accoutrements, broken muskets, hats, caps, cartridge paper, fragments of clothing.