James Polk and the Events that Led to the Mexican War

FROM THE LECTURE SERIES: A HISTORY OF THE UNITED STATES, 2ND EDITION

By Allen GuelzoPrinceton University

Two days after James Knox Polk’s inauguration, the Mexican envoy in Washington wrote to John C. Calhoun, who was then serving as secretary of state, to warn Calhoun that Texas was still regarded by Mexico as a Mexican province, that 11 years of Texan independence only amounted in Mexican eyes to a temporarily successful rebellion. He also added that Mexico would regard American annexation of Texas as an act of aggression and the most unjust.

US and Mexican flags
Mexico continued to consider Texas as its province which eventually led to the Mexican War. (Image: HelloRuby/Shutterstock)

Mexican Wrath

Polk had utterly mistaken the depth of Mexican anger over Texas. The American consul at Tampeko warned that the most stubborn and malignant feeling had come to occupy the mind of every Mexican against the United States.

The president of the Mexican republic—General José Joaquín de Herrera—saw little practical alternative to accepting the offers Polk made in negotiations concerning Texas. However, Herrera was also aware that anything that looked like a concession to the Americans would touch off an uprising in his own capital.

Polk Gives an Order

By that time, President Polk had begun to play catch up with events in Texas. In June of 1845, he ordered Brigadier General Zachary Taylor and 1,400 United States Cavalry and infantry to leave for the Texas border.

That sounds like a simple order, but in fact it wasn’t, and that was largely because there was a good deal of uncertainty as to what the Texas border was. The Mexicans insisted that the southern boundary of the Texas province had rested on the Nuasis River at Corpus Christie. The Texans insisted just as roundly that the southern boundary of Texas was the Rio Grande River 150 miles further to the south.

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Confrontation Begins

General Taylor avoided inflaming this dispute by setting up camp along the Nueces, and using the next several months there to drill his ill-trained troops, rather than going and looking for a confrontation with the Mexicans.

In February of 1846, though, Taylor was ordered to take his men down to the Rio Grande and establish his encampment there at Matamoros, to enforce the idea that the Rio Grande was the boundary.

signboard with Texas state line written
The Texan borderline was a much debated topic. (Image: Photo.Ua/Shutterstock)

So, on March 8, Taylor sent the advance elements of his little army dragoons and artillery on the road to Mateo Morose.

American Retaliation

En route, Taylor collided with several scouting parties of Mexican soldiers, and when he reached Matamoros he fortified his camp against any chances. On April 24, an American scouting party was ambushed by Mexicans, and on April 30, a Mexican army of about 5,000 men began crossing the Rio Grande, and surrounded Taylor’s encampment. Taylor brought up 2,200 American reinforcements and on May 8, he marched out to offer battle to the Mexicans, who were now under the command of General Mariano Arista at Palo Alto.

The Mexicans had the advantage of numbers, but against Taylor’s artillery the Mexican infantry hurled themselves in vain. The next day, the Mexicans fell back toward the Rio Grande, but Taylor pursued them and caught up with the Mexican retreat at Resaca de la Palma, about three miles from the Rio Grande River. There, Taylor went on the attack, driving the Mexicans from their position in panic.

Declaration of War

On the same day, May 9, word reached Washington from Zachary Taylor of the April 24 ambush, and on May 10, President Polk drafted a message to Congress asking for a declaration of war against Mexico, on the grounds that the Mexican army had attacked Taylor’s force without provocation, on land owned by the United States.

The Mexican War was compared to the Alamo and San Asinto, a relatively unglamorous affair. Neither Mexico nor the United States was prepared for war, and both nations stumbled into it with preparations half made.

An Ill-prepared US Army

The United States Army in 1846 amounted to only about 6,500 men present and ready for duty, organized into 16 regiments, and for all practical purposes, their tactical doctrine was almost unchanged from the Revolution and the War of 1812. In some cases, American regiments were even armed with castoff British Brown Bess muskets still on the old Revolutionary pattern.

Each infantry regiment was still organized into 10 companies, with two companies on each flank designated as light infantry and grenadiers. Almost half the United States Army were immigrants, and a large number of the senior generals had been commissioned as officers before the War of 1812; most of them had never maneuvered any body of troops larger than a few companies.

To make matters worse, President Polk proposed to flesh out this tiny force by enlisting 50,000 new men, but he did it not by enlisting them directly into federal service in the regular United States Army. Instead, he did it by accepting regiments of state volunteers who would be uniformed and equipped by their individual states, and only issued weapons by the federal government.

Mexico’s Larger Army

By contrast, the Mexican army looked like it was the odds-on favorite to win the war. This was because the Mexican army was four times as large as the regular United States Army, and it had been in and out of combat much more than the Americans over the previous 25 years.

This surface professionalism, however, concealed the bleak reality that Mexico had no factories for producing weapons, and few facilities for clothing its troops. Its ranks were filled by conscription, not by volunteering and the ordinary Mexican soldier was a very tough nut to crack.

Ready or not, there was no question about the enthusiasm Americans displayed for the war, and there was also no question about the dread and resentment of the Mexicans at American claims on Texas.

Common Questions about James Polk and the Events that Led to the Mexican War

Q: What was the dispute about the Texan border?

There was a good deal of uncertainty as to what the Texas border was. The Mexicans insisted that the southern boundary of the Texas province had rested on the Nueces River at Corpus Christie. The Texans insisted just as roundly that the southern boundary of Texas was the Rio Grande River 150 miles further to the south.

Q: What ultimately led to the declaration of war against Mexico?

President Polk drafted a message to Congress asking for a declaration of war against Mexico on the grounds that the Mexican army had attacked Taylor’s force without provocation, on land owned by the United States.

Q: Where did General Taylor set up his camp?

General Taylor set up his camp along the Nueces to avoid any disputes.

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