On a broad coastal prairie at the tip of Texas near the mouth of the Rio Grande in 1846, U.S. and Mexican troops met on the Palo Alto Battlefield. This was the first battle of a war that would decide which country would hold much of the continent. The United States eventually prevailed in that conflict and forced Mexico to surrender a vast expanse of territory that extended from Texas to the Pacific Ocean. That territory also included thousands of Mexicans who owned property and lived into the ceded territories. As a result of the fighting that started at Palo Alto and the treaty that ended the war between the two nations, many Mexicans became citizens of the United States.

When James K. Polk campaigned for the U.S. Presidency in 1844, the role of Mexicans in the west was far from his mind. He wanted to expand the United States to the Pacific Ocean and viewed the annexation of Texas as an important first step toward that goal. Opponents cited numerous dangers of annexation, including the possibility that Mexico might fight the acquisition of its former territory. Although the Republic of Texas had separated from Mexico in 1836, Mexico had never recognized the split and had long vowed to retake the wayward province.

The American people ignored these warnings. Many believed that it was their nation’s “Manifest Destiny” to expand across the continent, and they turned out in numbers to vote Polk into office. This victory was seen as a mandate for westward growth and, even before Polk’s inauguration the U.S. Congress extended an offer of statehood to Texas. Mexico responded by severing political ties with the U.S.

When the new President finally took office in March of 1845, he declared that the new state extended from the source of the Rio Grande in the Rocky Mountains to the mouth of that river on the Gulf coast. This caused additional clamor to the south. Mexicans had always drawn Texas as a much smaller territory, bounded in part by the Nueces River. They saw Polk’s boundary claim as an effort to take even more of their nation. He demanded that Mexico sell other territories extending to the Pacific Ocean, which reinforced this opinion.

In July 1845, President Polk ordered General Zachary Taylor and his troops to report to Corpus Christi and protect settlers in Texas from an imminent Mexican attack Courtesy of the National Park Service

In the fall of 1845, Polk sent envoy John Slidell to Mexico City to negotiate the Texas issues and the U.S. acquisition of the New Mexico and California territories. At the same time, the President sent an army commanded by General Zachary Taylor to Corpus Christi, near the mouth of the Nueces River. Taylor had orders to defend Texas from a possible Mexican invasion, but it was clear that Polk hoped the show of force would influence negotiations.

Mexican President Joaquin Herrera desperately wished to resolve the Texas dispute, but Polk’s additional demands made it politically impossible for him to receive the U.S. envoy. As Herrera struggled to find a solution to the rift with the U.S., General Mariano Paredes y Arrilla marched an army into Mexico City and overthrew the President. Just days after Texas formally became the 28th U.S. state, Paredes declared himself interim president and vowed to resist all demands by the United States.

The dispute moved rapidly into a military phase. In response to Paredes’s strong words, Polk ordered Taylor and his army to occupy the banks of the Rio Grande and claim the river as the nation’s southern border. In March 1846, Taylor established a fort across from the Mexican city of Matamoros. Mexican troops rushed to counter this move and by late April two large armies faced each other across the Rio Grande.

War erupted on April 25, when Mexico sent troops under Mexican General Mariano Arista across the Rio Grande and attacked a U.S. scout party at Rancho de Carricitos. Arista justified the attack as one of national defense, but Polk would make the same claim. After learning of the clash, the U.S. President declared that Mexican troops had shed the blood of American soldiers and, on May 13, the U.S. declared war.

That war was already well underway. Following the initial clash, General Arista attempted to surround and cut off the U.S. base on the Rio Grande. General Taylor anticipated the move and marched most of his troops to a coastal supply depot before Arista could seal the cordon. When that siege began on May 3, only about 500 U.S. troops remained in the fort that was commonly known as Fort Texas.

On May 7, General Taylor, at the head of 2300 troops, marched to lift this siege and, on May 8, General Arista, with 3200 men blocked his path at Palo Alto. In the fierce cannon battle that followed, the Mexican army suffered devastating casualties from the superior U.S. artillery. Although Arista’s troops held their ground until nightfall ended the clash, more than 100 Mexican soldiers died; even more were wounded.

Living historians load a replica cannon Courtesy of the National Park Service

Under cover of darkness, Arista fell back to the Resaca de la Palma, a wooded ravine about five miles south of Palo Alto. There, on May 9, he again attempted to halt the U.S. advance. But his demoralized troops broke quickly under the U.S. pressure and fell back. As U.S. troops moved on to liberate their fort, Arista’s soldiers fled for the safety of the Rio Grande and Matamoros. Days later, they abandoned Matamoros as well and opened that city to U.S. occupation.

The initial battles of this war were influential in conflict that followed. Devastated in the first clash at Palo Alto, the Mexican army never recovered. Although soldiers fought on for almost two years, Mexican forces lost battle after battle until U.S. troops held control of their capital city in September 1848. Forced to the negotiating table, Mexican officials fought to preserve territory, but eventually surrendered claims to Texas, recognized the Rio Grande as a boundary, and sold Mexico’s vast New Mexico and California territories to the United States.

With a stroke of a pen, on February 2, 1848 much of northern Mexico became the western United States. At the same time, the Mexican citizens who lived on that land became U.S. citizens. Many of these people never heard of the battle at Palo Alto, but the afternoon-long affair had an enormous impact on their future and on these new Mexican-Americans and the many generations to follow.

At the Palo Alto Battlefield National Historical Park today, visitors can come to the visitor center to watch an orientation video and view exhibits detailing the history of Palo Alto and the U.S.-Mexican War. Outside of the visitor center, tourists can take the half-mile walk to an overlook of the battlefield site. The park also offers extensive school activities, including a Student Ranger service-learning program for high school students.