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Mexican-American War
Cause, War, Resolution
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CAUSE

According to the Britannica website, the Republic of Texas had won de facto independence from Mexico in the Texas Revolution, which took place from 1835 to 1836. This included the battle of the Alamo, which took place from February 23 to March 6, 1836.

The U.S. annexed the Republic of Texas in 1845. U.S. diplomatic efforts to establish agreement on the Texas-Mexico border and to purchase Mexico's California and New Mexico territories failed. Mexico claimed that  Texas ended at the Nueces River; the U. S. Claimed that it ended at the Rio Grande. The war resulted in the United States’ acquisition of more than 500,000 square miles of Mexican territory extending westward from the Rio Grande to the Pacific Ocean.

Mexico severed relations with the United States in March 1845, shortly after the U.S. annexation of Texas. In September, expansionist U.S. President James K. Polk sent John Slidell on a secret mission to Mexico City to negotiate the disputed Texas border, settle U.S. claims against Mexico, and purchase New Mexico and California for up to $30 million. Mexican President José Joaquín Herrera, aware in advance of Slidell’s intention of dismembering the country, refused to receive him. When Polk learned of the snub, he ordered troops under General Zachary Taylor to occupy the disputed area between the Nueces and the Rio Grande; this took place in January 1846.

WAR

On May 9, 1846, Polk began to prepare a war message to Congress, justifying hostilities on the grounds of Mexican refusal to pay U.S. claims and refusal to negotiate with Slidell. That evening he received word that Mexican troops had crossed the Rio Grande on April 25 and attacked Taylor’s troops, killing or injuring 16 of them. In his quickly revised war message - delivered to Congress on May 11 - Polk claimed that Mexico had “invaded our territory and shed American blood on American soil.” Congress overwhelmingly approved a declaration of war on May 1.
When war broke out, former Mexican president and general Antonio López de Santa Anna (the vanquisher of the Texan forces at the Alamo in 1836) contacted Polk. The U.S. president arranged for a ship to take Santa Anna from his exile in Cuba to Mexico for the purpose of working for peace. Instead of acting for peace, however, on his return, Santa Anna took charge of the Mexican forces.

Following its original plan for the war, the United States sent its army from the Rio Grande, under Taylor, to invade the heart of Mexico while a second force, under Colonel Stephen Kearny, was to occupy New Mexico and California. Kearny’s campaign into New Mexico and California encountered little resistance, and the residents of both provinces appeared to accept U.S. occupation with a minimum of resentment. Meanwhile, Taylor’s army fought several battles south of the Rio Grande, captured the important city of Monterrey, and defeated a major Mexican force at the Battle of Buena Vista in February 1847. But Taylor showed no enthusiasm for a major invasion of Mexico, and on several occasions he failed to pursue the Mexicans vigorously after defeating them. In disgust, Polk revised his war strategy. He ordered General Winfield Scott to take an army by sea to Veracruz, capture that key seaport, and march inland to Mexico City. Scott took Veracruz in March after a siege of three weeks and began the march to Mexico City. Despite some Mexican resistance, Scott’s campaign was marked by an unbroken series of victories, and he entered Mexico City on September 14, 1847. The fall of the Mexican capital ended the military phase of the conflict.

RESOLUTION

Polk had assigned Nicholas Trist, chief clerk in the State Department, to accompany Scott’s forces and to negotiate a peace treaty. But after a long delay in the formation of a new Mexican government capable of negotiations, Polk grew impatient and recalled Trist. Trist, however, disobeyed his instructions and on February 2, 1848, signed the Treaty of Guadalupe Hidalgo. According to the treaty, which was subsequently ratified by both national congresses, Mexico ceded to the United States nearly all the territory now included in the states of New Mexico, Utah, Nevada, Arizona, California, Texas, and western Colorado for $15 million and U.S. assumption of its citizens’ claims against Mexico.


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