It’s popular in academe today to describe the Mexican War as an example of an aggressive and expansive colossus beating up on a weak neighbor, but that was not the case in 1846. The war was really a second phase of the Texas Revolution. Most people don’t understand that Mexico never recognized Texas independence. It is, however, well understood that Mexican President and Gen. Antonio Lopez de Santa Anna was defeated and captured at the Battle of San Jacinto by the Texas rebel Gen. Sam Houston on April 21, 1836. Santa Anna signed the Treaty of Velasco, which recognized Texas independence and established the Rio Grande as the boundary of Texas. Later, though, Mexico repudiated the treaty. This had little effect on the newly established Republic of Texas, which was recognized by the United States, Great Britain, France, and Belgium, among other countries.
For nearly ten years the Republic of Texas remained an independent country. Then, in 1845, negotiations began over annexation of Texas by the United States. Mexico announced that Texas was not an independent republic but Mexican territory under the rule of a rebel government, and that U.S. annexation of Texas would be an act of war. When the United States offered Texas a formal treaty of annexation, Mexico recalled her ambassador from Washington. Mexico also threatened to invade Texas and reconquer the former province.
Such public indignation and threats played well at home and were good for Mexican pride, but Mexico was at the same time quietly negotiating with Texas officials, offering formal recognition of Texas independence in return for a guarantee that Texas would remain independent of the United States. This was all too little, too late. Most Texans thought that the defeat of Santa Anna and the Treaty of Velasco had settled the issue of independence a decade earlier.
On the Fourth of July 1845—the choice of the date was not accidental—a specially convened Texas convention accepted the U.S. annexation offer. In November the voters of Texas overwhelmingly affirmed the decision. On December 29, Congress formally admitted Texas to the Union.
Meanwhile, the governments of the Republic of Texas and the United States had taken Mexican threats of war seriously and had agreed that the United States would begin stationing troops along the border with Mexico. First to arrive was Brig. Gen. Zachary Taylor, “Old Rough and Ready,” with some 2,000 men. Virginia-born but Kentucky-reared and a veteran of the War of 1812 and several Indian wars, Taylor got his nickname because he willingly endured every hardship that his troops endured, eating and sleeping with them and fighting alongside them.
In January 1846, Taylor established a camp at Corpus Christi, near the mouth of the Nueces River. Corpus Christi in those days was not much more than a trading post built in 1839 by Henry Kinney. In March 1846, Taylor moved down the Texas gulf coast and established a supply depot at Point Isabel, on the Texas side of the Rio Grande on the shore of the Gulf. About 20 miles further upstream he began the construction of a fort, which would become known as Fort Taylor or Fort Texas, and later Fort Brown. Francisco Mejia, the Mexican military commander at Matamoros, a Mexican town on the south bank of the Rio Grande, responded by making threats and demanding Taylor withdraw.
Taylor informed the Mexicans that the President of the United States had ordered him to take up a position on the American side of the Rio Grande and that he would leave only when ordered to do so by the President. He further stated that his actions were defensive only and he had no hostile intent. The Mexicans claimed that the mere presence of American troops was a hostile act, forgetting that there were Mexican troops massed on the south bank of the Rio Grande and that Mexico had said that a state of war had existed ever since the United States annexed Texas. Taylor declared that if war began, the responsibility for it would lie with whoever fired the first shot, something he said he would not do.
On April 10, 1846, Col. Trueman Cross, a veteran and highly respected officer, failed to return from horseback riding near the American camp at Point Isabel. Several days later his remains were discovered. He had been shot and stabbed. This might have been the incident that started the war, but General Taylor responded cautiously, saying it could have been the work of Mexican civilians. Across the border some 7,000 Mexican troops were massed, triple the number of American troops with Taylor.
On April 24, 1846, Mexican commander Gen. Mariano Arista sent a letter to Taylor, declaring it was only a matter of time before Mexican forces would cross the Rio Grande and attack what Arista called the American “Army of Occupation.” Some historians have argued that the United States was, in fact, occupying Mexican territory—that region of Texas called the Nueces Strip. The Nueces Strip was a triangular slice of territory lying between the Nueces River and the Rio Grande, the land between Corpus Christi and Brownsville. The problem with the argument is twofold. First, all Mexican settlements, except Laredo, had been established on the south bank of the Rio Grande—and Laredo was relocated to the south bank in 1771. The Rio Grande, without question, was the frontier line for Mexico. Later, when a few Mexican settlements were established in Texas, they had nothing to do with the Nueces River.
More importantly, though, the Treaty of Velasco, which Santa Anna had accepted, followed historical and geographical realities in establishing the Rio Grande as the Texas border. When Mexico later repudiated the treaty, she did not do so because the border was established at the Rio Grande but because she claimed all of Texas was still part of Mexico. The repudiation of the Treaty of Velasco had nothing to do with the Nueces Strip.
On April 25, the day after sending his threatening letter to Taylor, General Arista sent 2,000 of his men across the Rio Grande. They attacked a troop of patrolling U.S. dragoons (later known as cavalry troopers) and killed 14 of them. Two others later died of their wounds. Because the cavalry patrol was led by Capt. Seth Thornton, the incident is known as the “Thornton Affair.” General Taylor did not take any immediate action but sent a report of the Thornton Affair to President Polk. The report was received in Washington on the evening of Saturday, May 9. Polk consulted with his Cabinet on Sunday and addressed a joint session of Congress on Monday, saying, “Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon American soil.” He then called for a declaration of war against Mexico.
Polk could count on his own Democrats, who were in the majority, to support him, as well as most of the opposition Whigs. On Wednesday, May 13, the House voted 174-14 for a declaration of war. The Senate did likewise, 40-2. In both the House and the Senate the only opposition came from the most radical of the abolitionists, who had also fought against admission of Texas to the Union. They were against anything that might contribute to the support or expansion of slavery.
Mexican leaders were confident that, in a war with the United States, Mexico would prevail. President Paredes grandly predicted that Mexico would soon not only have Texas back but occupy New Orleans and control the entire Gulf Coast. Such remarks were not entirely idle boasting. Mexico had an army of 32,000. At the outbreak of the war the United States had a standing army of only some 6,000. Mexican troops were armed with the latest European firearms and artillery pieces, were trained and disciplined, and had years of experience fighting in one revolution after another. (During the 20 years leading up to the Mexican War there were 27 different Mexican regimes in power, usually put there by force of arms. One year saw three different regimes come and go.) Some American troops had fought in Indian wars, but the Army hadn’t gone up against a European-style fighting force since the War of 1812. Mexico also had the logistical advantage. The fighting would be on a distant southwestern frontier for the United States but at home for Mexico. While the United States later became the principal, even overwhelming, power of the Americas, it’s important to remember that in 1846 many were betting on Mexico.
Following the ambush of Captain Thornton and his cavalry troopers, General Taylor received intelligence that the Mexicans were preparing to attack his supply depot at Point Isabel. On May 1, Taylor left some 300 troops behind to garrison Fort Texas and marched to Point Isabel with the bulk of his forces, about 2,000 men.
Taking advantage of Taylor’s absence, a Mexican army of more than 5,000 men began a siege and bombardment of Fort Texas, which continued for six days. Although greatly outnumbered and suffering from an artillery pounding, and having lost the fort’s commander, Maj. Jacob Brown, the garrison refused to surrender. General Taylor would rename the fort in Major Brown’s honor. The Texas town of Brownsville also derives its name from the fort’s commander.
Meanwhile, Taylor completed loading all of his supply wagons at Point Isabel and began the march back to Fort Texas on May 7, with his 2,000 troops. The next afternoon, Taylor found the road to Fort Texas blocked at Palo Alto by the 5,000-man Mexican army, under the command of General Arista. What took place next was the first major battle of the Mexican War. The battle quickly became an artillery duel and raged until late in the day when the Mexican Army retreated, having suffered heavy casualties. Chalk up one victory for the Americans, although the much larger Mexican army was still very much intact and ready to fight again.
On May 9, the two armies clashed again, this time at Resaca de la Palma. The Mexicans were firmly entrenched along a long, shallow stream and hidden in dense chaparral. Artillery again played an important role, but so, too, did infantry and dragoons. The Mexican army again suffered heavy casualties, and the Mexicans were driven not only from the field of battle but back across the Rio Grande into Mexico. General Arista’s victory meal, which was being prepared at his camp in anticipation of success, was eaten by American soldiers. (Talk about eating the other guy’s lunch!)
General Arista and his troops were stunned by the upset victories of the smaller American force and a week later abandoned Matamoros and withdrew to Monterrey, 175 miles to the west. On May 18, 1846, General Taylor moved his army into Matamoros, occupying Mexican territory for the first time.