The Mexican War

When the United States Waged War Against Mexico It Gained Vast Territory

In the mid-1840s, relations between the United States and Mexico were strained. Texas was on the verge of becoming part of the US, and Mexicans were outraged.

The bad feelings intensified, violent conflicts erupted, and a bellicose American president quickly convinced Congress to declare war.

The actual conflict would be overshadowed by the Civil War two decades later. Yet it had profound consequences as the size of the United States increased with the addition of the southwest and California.

The Mexican War was also a valuable training ground for American officers who would later serve in the Civil War.

Factors Leading to the Mexican War

General Zachary Taylor
General Zachary Taylor. Library of Congress
  • Texas was an independent nation for nearly a decade, from 1836 to 1845.
  • Several nations, including the United States, Great Britain, and France recognized Texas as a nation.
  • Mexico refused to accept that Texas was independent, and would not recognize it.
  • When the United States offered to annex Texas, Mexico considered it tantamount to an act of war.
  • Mexico threatened to invade Texas and reclaim it. The United States stationed an army led by General Zachary Taylor in Texas to defend it.
  • In late 1845, an American ambassador was accepted by the Mexican government as both sides seem to try to avoid open warfare.

War Declared After First Skirmishes

US Dragoons Battle Mexican Ambush
US Dragoons Battle Mexican Ambush. Library of Congress
  • In January 1846, President James K. Polk ordered General Taylor to take up a defensive position along the Rio Grande.
  • Throughout the spring of 1846, tensions increased along the border.
  • On April 25, 1846, Mexican troops ambushed a squad of United States dragoons. Fourteen Americans were killed.
  • General Taylor sent a report to Washington, which was received by President Polk on May 9.
  • On May 11, Polk addressed a joint session of Congress, calling for war.
  • On May 13, the Congress declared war on Mexico.
  • On May 7, the American Army commanded by General Taylor had fought a battle with the Mexicans, so the first full battle of the war actually happened before the official declaration.

Mexican War Popular With the Public

  • The war with Mexico was wildly popular with the American public, and thousands of men rushed to recruiting stations to join the US Army.
  • There was some dissent against the war. New England abolitionists saw the war as an attempt to add a slave state, Texas, to the Union.
  • Abraham Lincoln, then an obscure member of the House of Representatives, opposed the war.
  • In Concord, Massachusetts, a little-known writer, Henry David Thoreau, protested the war by refusing to pay a local tax. He was arrested and spent a night in jail (a relative paid his tax, against Thoreau's wishes). Thoreau wrote his famed essay "Civil Disobedience," urging others opposed to the war to follow his example.

The War Begins in Earnest

Zachary Taylor at Buena Vista
Zachary Taylor at the Battle of Buena Vista. Library of Congress
  • General Taylor's forces crossed the Rio Grande, entering Mexico, and eventually conquered most of northern Mexico.
  • The US Navy played a vital, though sometimes overlooked, role in the Mexican War. In the summer of 1846, for instance, naval forces occupied Monterey, California, which at the time was Mexican territory.
  • On February 22-23, 1847, General Taylor's forces defeated a Mexican army at the Battle of Buena Vista. The engagement made Taylor a national hero and would ultimately propel him to the White House.
  • During the battle, Taylor instructed an artillery captain to fire deadly grape shot at the Mexican troops. "A little more grape, Captain Bragg" was widely quoted in newspapers and was even immortalized in popular lithographs.

American Victories Continue

Storming of Chapultepec
Lithograph of Storming of Chapultepec. Library of Congress
  • At the Siege of Veracruz, which took three weeks in March 1847, American forces made their first major amphibious landing in history.
  • The fortress at Veracruz was considered to be nearly impregnable, but it fell to American forces who managed to surround it.
  • In the summer of 1847, the US Army, under the command of General Winfield Scott, began moving toward Mexico City.
  • On September 13-14, American forces defeated the Mexicans at the Battle of Chapultepec, a castle near Mexico City. The "Halls of Montezuma" mentioned in the "Marines' Hymn" immortalized the battle.
  • A young lieutenant, Ulysses S. Grant fought in the battle, as did a young captain, Robert E. Lee. They would, of course, command entire armies in the Civil War.

Mexico City Falls to the Americans

Scott Enters Mexico City
General Scott Enters Mexico City. Library of Congress
  • Fighting around Mexico City continued from September 12 to September 15, when American forces entered the city.
  • An American Marine hoisted the Stars and Stripes over the National Palace. General Winfield Scott later entered the city as American bands played in triumph.
  • About 1,500 Americans were killed in the battle for Mexico City.
  • With the capture of the Mexican capital, the war was effectively ended.

The United States Gains Territory

  • The Mexican War officially ended with the Treaty of Guadalupe Hidalgo, which was signed on February 2, 1848.
  • The treaty ended hostilities, and included provisions that greatly increased the size of the United States.
  • The border between the US and Mexico was fixed as the Rio Grande River, and the US took undisputed control of Texas.
  • The US also gained the present day states of Utah, Nevada, and California.
  • Parts of New Mexico, Arizona, Colorado, and Wyoming which had been part of Mexico became American territory.
  • The acquisition of so much territory outraged critics of the war.

Legacy of the War

Zachary Taylor Poster
Zachary Taylor Campaign Poster, printed in summer 1847. Library of Congress
  • The Mexican War was a valuable training ground for American officers, many of whom would later serve in the Civil War. When Lee met Grant at Appomattox in April 1865, they had a friendly conversation about service in Mexico.
  • Zachary Taylor, the hero of Buena Vista, would return to the United States and pursue a political career. Posters promoting him as a presidential candidate began appearing in the summer of 1847. He ran for president on the Whig ticket in 1848 and was elected. Inaugurated in March 1849, he died in office in July 1850.
  • Debate about the cause of the Mexican War has never faded. Some scholars contend that expansionist American leaders wanted to provoke the war to gain territory, including California in particular.
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Your Citation
McNamara, Robert. "The Mexican War." ThoughtCo, Jun. 18, 2014, McNamara, Robert. (2014, June 18). The Mexican War. Retrieved from McNamara, Robert. "The Mexican War." ThoughtCo. (accessed December 15, 2017).