Mexican-American War
1846-48
The Mexican-American War was an armed military conflict between the United States and Mexico from 1846 to 1848 in the wake of the 1845 U.S. annexation of Texas. Mexico did not recognize the secession of Texas in 1836; it considered Texas a rebel province.
In the United States, the war was a partisan issue with most Whigs opposing it and most southern Democrats, animated by a popular belief in the Manifest Destiny, supporting it. In Mexico, the war was considered a matter of national pride.
On April 21, 1836, the Texans decisively defeated Santa Anna's forces in the Battle of San Jacinto. Santa Anna himself was taken captive by the Texas militia forced to sign the Treaties of Velasco in which he promised to recognize the sovereignty of the Republic of Texas and the Rio Grande as the boundary between Texas and Mexico.
The Mexican government, however, refused to acknowledge these concessions, arguing that Santa Anna was not a representative of Mexico, that he had no authority to negotiate on behalf of Mexico, and that he signed away Texas under duress. The Mexican government never ratified the Treaties of Velasco, but did not reopen the war.
Mexico claimed the Nueces River — about 150 miles (240 km) north of the Rio Grande — as its border with Texas; the United States claimed the Rio Grande as the boundary, citing the 1836 Treaty of Velasco. Mexico, however, never ratified this treaty. Regardless, the United States used the treaty to advance its cause.
In 1846, after Texas was admitted into the Union, Polk sent militia under General Zachary Taylor to the Rio Grande to protect Texas. Taylor ignored Mexican demands to withdraw to the Nueces.
On April 24, 1846, a 2,000-strong Mexican cavalry detachment attacked a 63-man U.S. patrol that had been sent into the contested territory north of the Rio Grande and south of the Nueces River. The Mexican cavalry succeeded in routing the patrol.
President Polk had received word of the attack and told Congress on May 11, 1846 that Mexico had "invaded our territory and shed American blood upon the American soil." A joint session of Congress approved the declaration of war.
In the United States, most Whigs in the North and South opposed the war; most Democrats supported it. Joshua Giddings led a group of dissenters in Washington D.C. He called the war with Mexico "an aggressive, unholy, and unjust war," and voted against supplying soldiers and weapons for the war.
In the end the American military under General Winfield Scott occupied Mexico City where they forced the Mexican government to sign the Treaty of Guadalupe Hidalgo, on February 2, 1848. The treaty ended the war and gave the U.S undisputed control of Texas, established the U.S.-Mexican border of the Rio Grande River, and ceded to the United States the present-day states of California, Nevada, Utah, and parts of Colorado, Arizona, New Mexico, and Wyoming.
The treaty gave Mexico US $15,000,000 — less than half the amount the U.S. had attempted to offer Mexico for the land before the opening of hostilities.
The acquisition was a source of controversy at time, especially among U.S. politicians that had opposed the war from the start. A leading U.S. newspaper, the Whig intelligencer sardonically concluded that:
“We take nothing by conquest.... Thank God.”