Though successful, Mexican war brought guilt


The Annexation of Texas in 1845 precipitated a major crisis in relations between Mexico and the United States. During the political campaign of November 1844, it became evident that the Democratic strategy was that the borders of the United States should be expanded. The real issue was whether or not the electorate was willing to follow the dictates of “manifest destiny” beginning with Texas and Oregon and ending no one knew quite where.

President Andrew Jackson had recognized Texan independence in 1837, but fearing the addition of another slave state to the Union, antislavery forces successfully blocked efforts to annex the Texas Republic. In 1843, President Santa Anna of Mexico warned that the United States annexation of Texas, which Mexico still claimed sovereignty, would be equivalent to a declaration of war.

Not to be bullied, President Sam Houston of the Texas Republic accepted the United States’ offer for annexation on the condition the military and naval protection would be forthcoming as a defense against Mexican invasion. The Senate, in a pacifist/antislavery spirit, rejected the proposal annexation.

Polk victorious

In the final days of May 1844, the Democratic Party convention, meeting in Baltimore, nominated a Tennessee political leader who was an ardent annexationist and a close friend of Jackson, named James K. Polk. With potent backing from slaveholding states, he made Texas and Oregon annexation the center of his campaign and scored a narrow victory over the Whig candidate Henry Clay of Kentucky. Viewing Polk’s victory as a mandate for Texas annexation, President John Tyler, whose four-year administration was a “bed of thorns” and who the Whigs came to hate, recommended that the “lame duck” Congress pass a joint resolution to annex Texas. Congress did it and Tyler signed it on March 1, 1845, three days before Polk’s inauguration.

Mexico immediately broke off diplomatic relations with the U.S., and Polk came to office with half of his foreign policy virtually accomplished.

Border dispute

The flashpoint of controversy now was whether the Nueces River formed the southern border of Texas as Mexico believed, or the Rio Grande, 130 miles further south, as the Polk administration insisted.

In the middle of June 1845, Polk ordered Brig. Gen. Zachary Taylor to move his “Army of Observation” into the disputed area. By summer’s end, he had established a base on the south bank of the Nueces near Corpus Christi. This show of force convinced the Mexicans to request a meeting to discuss the boundary. Polk dispatched John Slidell, a Louisiana politician, to Mexico on a secret mission to deliberate the border question and with three other instructions to add to the discourse.

Slidell was to inquire about the purchase of California for $25 million, New Mexico for $5 million and the payment of damages to American nationalists for losses incurred in the Mexican revolutions. When Slidell reached Mexico City Dec. 6, the Mexican government refused to accept his offering. A government coup resulted in a new president: Gen. Mariano Paredes y Arrillaga. He reaffirmed Mexico’s claim to Texas and also refused to talk to Slidell who returned to the U.S. with nothing accomplished.

War inevitable

Long before Slidell returned, Polk had decided that war was inevitable if he were to get all the territory necessary to round out the natural boundaries of the U.S. The Pacific Ocean was the logical end of manifest destiny.

On April 25, 1846, the two countries came face to face. A large Mexican force crossed the Rio Grande and surrounded a small American reconnaissance party. When the Americans attempted to break out of the encirclement, 11 Americans were killed and 26 were captured, including Capt. Seth Thornton.

Polk delivered a declaration of war against Mexico to Congress May 11, 1846. By a vote of 174-14, Congress supported the request because “Mexico had shed American blood upon American soil.” It was fortunate that Congress approved because Taylor had already fought and won the battles of Palo Alto and Resaca de la Palma and was in Matamoros by May 18, 1846.

Polk’s strategy was to occupy Mexico’s Northern provinces, blockade Mexican ports and conquer New Mexico and California before England and Russia did. By September of 1846, Taylor’s army had taken Monterrey and controlled northern Mexico, and by January 1847, American forces in the West led by Col. Stephen Kearny had secured New Mexico and California. Although successful militarily, the strategy failed to bring Mexico to terms.

Polk decided to shift the military efforts to the heart of the country — Mexico City. In March 1847, following a week of naval bombardment of Vera Cruz, “old fuss and feathers” Gen. Winfield Scott started his army along the National Road toward the Valley of Mexico. By September, he had control of the capital by defeating the returned leader of Mexico, Gen. Santa Anna.

When the Mexican government fled, the American troops lingered as an occupational army for some 10 weeks while the politicians hammered out the Treaty of Guadalupe Hidalgo. The treaty accepted the Rio Grande as a boundary between Texas and Mexico, and also ceded New Mexico, California and the territory that lay between them. The U.S. made a cash payment of $15 million to Mexico. Mexico’s one stroke of good fortune was that America’s dream of manifest destiny, that included annexing all of Mexico, was smashed by anti-slavery fears of spreading the “peculiar institution” into additional lands.

Enthusiasm weakens

In the beginning, the war was popular, and the country was seemingly enthusiastic about the acquisition of new territory. But enthusiasm soon weakened. The attack on Mexico was criticized as unworthy of the nation’s honor. Anti-slavery supporters were sure that a southern conspiracy exited to extend slavery limits. Democrats were charged with fermenting war to gain glory and win the election of 1848. Finally, the anti-war faction saw it as a political war and Abraham Lincoln agreed.

The war left Mexico divided, discouraged and bereft of an immense amount of territory. It was a national calamity, and Mexico has never forgotten it. For the U.S., the war was spectacularly successful both militarily and diplomatically. It was a training exercise for the American Civil War. Unlike the American Revolution, Civil War and World Wars I and II, this war has never really caught the fancy of the American public. One reason for the apparent indifference is that the Mexican War was so blatantly an offensive war that we have come to feel guilty about it.

That’s your history!


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Professor Emeritus Hugh Earnhart had a 32-year career in the history department at Youngstown State University, where he specialized in the Civil War and the South. Send suggestions, comments or questions to Hugh Earnhart in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460-0038; or via email to:



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