The Mexican War was a brief yet significant event in the history of the United States. In eighteen months of fighting, the U.S. Army won a series of decisive victories and captured nearly half of Mexico's territory. In the end, the conflict added some one million square miles of land to the young nation, including the valuable deep-water ports of coastal California.
A period of distrust and misunderstanding preceded the opening of hostilities between the United States and Mexico. After gaining its independence from Spain in 1821, Mexico controlled most of the land north of the Rio Grande that encompasses the present-day states of Texas, New Mexico, Arizona, and California. Between the 1820s and 1840s, English-speaking settlers filtered into this area, which was only marginally controlled by the overextended government in Mexico City.
Thousands of Americans, who changed their citizenship and received large tracts of land from the Mexican government, rebelled in Texas in 1835 for several reasons, including Mexico's abolition of the locally popular Texas provincial government and its inability to protect the settlers against Indian raids. These infringements prompted some of the Mexicans living in the region to side with the rebels. Additional causes of the independence movement include cultural differences springing from the Protestant beliefs of the American immigrants and Mexican demands that all become Catholic. Many settlers, moreover, were from the southern states and wanted to introduce slavery into territory that had been free since 1821, an anathema to most Mexicans.
The rebels won their independence in 1836 and
formed the Republic of Texas. Mexico, however, refused to honor Texas'
independence granted by General Antonio Lopez de Santa Anna after the
battle of San Jacinto. Consequently, during their years as an
independent nation, the Texans did not have formal diplomatic relations
with Mexico. Texans insisted that their southern border was the Rio
Grande.
The Battle of Palo Alto (Spanish: Batalla de Palo Alto) was the first major battle of the Mexican–American War and was fought on May 8, 1846, on disputed ground five miles (8 km) from the modern-day city of Brownsville, Texas. A force of some 3,700 Mexican troops – most of the Army of The North – led by General Mariano Arista engaged a force of approximately 2,300 United States troops – the Army of Occupation led by General Zachary Taylor.
On April 30, following the Thornton Affair, Mexican General Mariano Arista's troops began to cross the Rio Grande. On May 3, the troops began to besiege the American outpost at Fort Texas. Taylor marched his Army of Occupation south to relieve the siege. Arista, upon learning of his approach, diverted many of his units away from the siege to meet Taylor's force. The battle took place on May 8, three days before the formal declaration of war on Mexico by the United States. Arista ordered two cavalry charges, first against the American right flank and later against the left. Both were unsuccessful. The American victory is widely attributed to superior artillery, as the U.S. "light" artillery was much more mobile and accurate than that of the Mexican forces.
That evening, Arista was forced to withdraw further south. The armies clashed again the next day at the Battle of Resaca de la Palma.
