The Mexican-American War

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Explore the Mexican American War more in-depth at Two Nations, One Border: U.S.-Mexican War, 1846-1848.

Battle of Vera Cruz. Painting by Carl Nebel, published in 1851 in The War Between the United States and Mexico, Illustrated

Once American blood had been shed, Congress acted and declared war on Mexico on May 12, 1846. The government fought the war in three major campaigns:

General George Kearney led his forces into New Mexico and California with the help of the American Navy and John C. Fremont’s troops, taking the state by January 1847.
General Zachary Taylor continued his advance into northern Mexico, taking Monterrey and winning the Battle of Buena Vista. Taylor’s victory proved significant because the Mexican Army was twice the size of the American force. Despite the overwhelming numbers, the Mexican troops lost to the Americans, securing all of Mexico’s northern territories for the United States.
General Winfield Scott led a final campaign into the heart of Mexico, planning to take Mexico City. Scott’s forces landed at Vera Cruz and marched inland, capturing the capital in September 1847 and ending the war.

Major General Winfield Scott, Currier and Ives lithograph, c. 1846

Antiwar Sentiment

Despite the victorious ending to the war, Polk faced political criticism at home because of the war’s beginnings. Abraham Lincoln, a young Congressman, declared that “the war with Mexico was unnecessarily and unconstitutionally commenced by the president.” Congressman Alexander Stephens, future vice-president of the Confederacy, said that the “principle of waging war against a neighboring people to compel them to sell their country is not only dishonorable, but disgraceful and infamous.” But most Americans rejoiced that the war was over and had resulted in such a favorable settlement for the United States.

Treaty of Guadalupe-Hidalgo 1848

The defeated Mexicans were pressured to sign the Treaty of Guadalupe Hidalgo. In this treaty Mexico gave up all claims to Texas and sold the rest of what became the American Southwest (which was a little more than half of the country of Mexico) to the United States for $15 million. The United States also agreed to assume the claims American citizens had made against the Mexican government for the destruction of American property, an amount over $3 million. The treaty set the border between the countries as the Rio Grande. In the United States Congress, ratification of the treaty was contested along party lines. Whigs did not want any of the land to become United States property (fearing a growth in both slavery and Democratic power) and the Democrats wanted to seize all of Mexico. The parties finally compromised and ratified the original treaty, except for parts that guaranteed protection of Mexican property rights.

Legacies of the Mexican-American War

Though the war with Mexico was short, it had many important legacies. Here are a few:

The war cost $98 million
1,700 men were killed in battle
4,000 men were wounded
11,000 men died of disease
The war trained young officers for the more important Civil War to come in thirteen years, including men like Jefferson Davis, Robert E. Lee, Ulysses S. Grant, and George McClellan.
The United States acquired over a million square acres of land, including the Pacific harbors of San Diego, Monterrey, and San Francisco.
The acquisition of this territory completed the present borders of the United States, except for a small parcel of land acquired in 1853 from Mexico through the Gadsden Purchase (1853), which was needed to build the proposed southern transcontinental railroad.
On a negative note, the acquisition of the new territories sent a wave of disputes through Congress over whether slavery would be allowed to extend into the new land. These disputes hastened the Civil War.
The Mexican War never took on the dimension of a moral crusade based on the defense of democratic principles. The United States did not fight for independence, freedom for oppressed peoples, or to save democracy. The United States waged the war in the name of expansion and Manifest Destiny to acquire more land.