In the Spring of 1846, disputes over the ownership and boundaries of Texas thrust the United States and Mexico into war.

On December 29, 1845, U.S. President James K. Polk fulfilled a long-standing campaign promise by welcoming the former Republic of Texas as the 28th state in the Union. But Mexicans insisted that Texas was rightfully part of their country. Although settlers in this territory had claimed independence from Mexico since 1836, Mexican leaders had never recognized Texan sovereignty and still harbored faint hopes of controlling the wayward province. They denounced the U.S. annexation as an act of aggression against Mexico.

Tensions heightened when U.S. President Polk announced that the Rio Grande formed the boundary of Texas. While Texans championed this river as their boundary, Mexico mapped Texas as a much smaller region--bounded in part by the Nueces River. Left in dispute was a huge expanse of land between the two rivers.

In July of 1845, Polk sent an army led by General Zachary Taylor to Corpus Christi, on the banks of the Nueces River. The troops were officially dispatched to help defend Texas from a potential Mexican attack on Texas. But they also represented a display of power as a U.S. negotiator headed to Mexico.

The advance of U.S. troops and Polk’s new demand that Mexico sell its New Mexico and California territories infuriated Mexican President Joaquin Herrera, who refused to meet with the American envoy. But Herrera’s willingness just to allow the envoy into Mexico brought about his downfall. In December of 1845, General Mariano Paredes y Arrillaga overthrew Herrera, installed himself as President, and vowed to discuss nothing but the return of Texas.

Polk continued to exert pressure. In January 1846, he ordered General Taylor to claim the Rio Grande as the U.S. boundary.In March, Taylor led 4,000 troops to the river’s edge, across from the Mexican city of Matamoros, and began construction of Fort Texas, the earthen fieldwork that would serve as a U.S. base.

General Paredes was not swayed by this show of force. He expelled the U.S. envoy from Mexico, declared his willingness to fight, and sent thousands of troops to the city of Matamoros. In April 1846, he appointed General Mariano Arista as the commander of this growing force.

The U.S. President hesitated to respond with hostilities against Mexico. Many political foes within the United States questioned his claims to the Rio Grande boundary, and Polk realized that a move to cross the Rio Grande or fire the first shots of war might sway public opinion against his cause. Instead, he waited for Mexican forces to initiate combat north of the river so that he could portray the conflict as one of national defense.

Mexican leaders viewed the U.S. occupation of the Rio Grande as an invasion deep into their territory and did not hesitate to cross the river. On April 25, 1846, Mexican troops overwhelmed a U.S. scout party on the north bank of the river, at Rancho de Carricitos. When word of this clash reached Washington D.C. on May 10, Polk announced that Mexico had "spilled American blood upon the American territory" and demanded a response. On May 13, 1846, as a spirit of nationalism swept away recent debates, Congress complied and declared war.

Battles on the Rio Grande

Combatants on the Rio Grande did not wait for this formal decree. With hostilities underway, Mexican General Arista began shuttling troops across the river to besiege the isolated U.S. post, Fort Texas. U.S. General Taylor expected just such a move. On May 1, 1846, he marched to Point Isabel, a portage area on the Gulf of Mexico to meet an incoming naval fleet carrying supplies needed to withstand a prolonged siege. He left behind Major Jacob Brown, the U.S. Seventh Infantry, and portions of the Third Artillery--some 550 men--to hold the post on the river.

Arista was not able to prevent Taylor’s departure for the coast, but moved quickly to surround the U.S. outpost. On May 3, 1846, Mexican artillery opened fire on Fort Texas from all directions, hoping to force a quick surrender of the defenders.

General Taylor soon marched to assist his besieged men.After pausing to improve defenses at his supply depot, known as Fort Polk, on May 7 he set out with 2,300 troops and 200 supply wagons to break the siege of Fort Texas.

General Arista moved to block this advance, positioning 3,200 troops across the Matamoros road as it crossed the broad prairie of Palo Alto. There, on the afternoon of May 8, 1846, he engaged the U.S. force in a fierce artillery battle--the first major clash of the war.

Map of Battles on the Rio Grande

Mexican forces stood their ground but suffered heavy casualties.And, on the morning of May 9, General Arista withdrew several miles to the brush covered banks of Resaca de la Palma.  Taylor’s troops pursued the Mexican forces and engaged them that afternoon in the battle of Resaca de la Palma. There, U.S. soldiers overran Arista’s lines, forced Mexican troops to retreat across the Rio Grande, and ended the six-day siege of Fort Texas.

On May 18, 1846, Taylor’s troops forded the Rio Grande and entered the city of Matamoros. The occupation took place without a fight. Mexican forces had determined that the city could not be defended and had withdrawn down the roadway leading to Monterrey. The lower Rio Grande Valley had been conceded to the U.S. Army.

An Extended War

In the aftermath of the battles on the Rio Grande, many U.S. soldiers felt certain that their success would produce an early end to war. Mexican leaders, however, remained determined to fight. Despite continuing U.S. pressure and a growing list of Mexican defeats, Mexican leaders came to view the conflict as a war of honor and resisted for almost two years.

In the summer of 1846, the war shifted west as army and naval forces began the conquest of Mexico’s New Mexico and Upper California territories that would reach completion in January 1847. But Zachary Taylor’s forces would remain at the forefront of activity.  After adding thousands of volunteer soldiers to his once-tiny force, Taylor left Matamoros in August 1846 and proceeded toward the Mexican interior.

The General's progress, however, was slow. Despite winning a five-day battle at Monterrey on September 25, 1846, occupying Saltillo on November 16, and overcoming two days of trial to gain an improbable victory over General Antonio Lopez de Santa Anna in the mountain pass of Buena Vista (or La Angostura) on February 24, 1847, Taylor frustrated President Polk, who wanted to secure a rapid end to the war. For this reason, in November 1846, Polk appointed General Winfield Scott as the new General-in-Chief of U.S. forces in Mexico and sent him to open a new front at the gulf coast city of Veracruz.

Winfield Scott’s campaign became the deciding factor in the war.  Landing near Veracruz, on March 9, 1847, he bombarded the city until military officials surrendered on March 29.  From there, Scott pressed toward central Mexico, defeating Mexican defenders at Cerro Gordo (April 18, 1847), Contreras and Churubusco (August 20, 1847), and Molino del Rey (September 8, 1847).  On September 13, 1847, the dramatic U.S. assault on the Mexican stronghold of Chapultepec overwhelmed the last major line of defense for Mexico City. The following day, U.S. troops entered the Mexican capital and raised the Stars and Stripes over the National Palace.

Peace and After

Even with U.S. troops occupying their capital city, Mexican leaders hesitated to surrender territory and negotiations dragged on for months. At last, however, on February 2, 1848, the United States and Mexico came to terms. In the treaty of Guadalupe-Hidalgo, Mexico agreed to surrender all claims to Texas and accept the Rio Grande as the boundary of that state. Mexico also agreed to sell its New Mexico and Upper California territories to the United States at a price of $15 million. The treaty effectively halved the size of Mexico and doubled the territory of the United States.

Map of Territory Transferred by Treaty

This territorial exchange had long-term effects on both nations. The war and treaty extended the United States to the Pacific Ocean, and provided a bounty of ports, minerals, and natural resources for a growing country. The abundance of lands also produced debates about extending slavery into the West, a dispute that would help spark a nation-defining civil war. In Mexico, the loss of battles and territories was a national trauma. As political and military leaders challenged each other on the best way to revive their troubled country, Mexico also descended into a long period of turmoil, civil war, and foreign intervention. But the war also inspired new leaders who were determined to avoid additional humiliation for their country. The new generation eventually united Mexico, forced out foreign invaders, and established the foundations of a modern state.

Perhaps the most enduring effect of the war, however, is on U.S.-Mexican relations.  While the war is recalled with passion south of the border, it is often overlooked to the north.  And, although the two countries have developed strong bonds and friendly ties since 1848, these neighbours continue to struggle with distrust and misunderstandings created by the war, its effects, and the differing approaches to remembering the conflict.

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The original text has been taken from Palo Alto Battlefield National Historic Site

Contact me by clicking here Richard Holling