Lesson 25: Mexican American War

James K. Polk

• U.S. president who pushed westward expansion.

• Sent John Slidell to buy CA & NM for $25M.

• Claimed Mexico “shed American blood upon American soil.”

• Asked Congress for war → Mexican-American War began (May 13, 1846).

• Whigs criticized conflict as “Mr. Polk’s War.”

John Slidell

• U.S. diplomat sent by Polk to Mexico.

• Mission: purchase California and New Mexico for $25 million.

• Mexico refused to receive or negotiate with him

Mexico

• Rejected Slidell’s diplomatic mission and offer.

• Claimed Texas border was the Nueces River instead of the Rio Grande.

• Mexican forces attacked Taylor's troops in disputed territory.

• Ultimately defeated; ceded territory in Treaty of Guadalupe Hidalgo

Nueces River

Border claimed by Mexico as northern Texas boundary.

Rio Grande River

• Border claimed by U.S. as southern Texas boundary.

• Basis of Polk’s claim that Mexico invaded U.S. soil.

Zachary Taylor

• U.S. general stationed between Nueces & Rio Grande.

• Mexican forces attacked his troops; 11 Americans killed (May 9, 1846).

• Incident used by Polk to justify going to war.

“shed American blood upon the American soil”

• Polk’s message to Congress claiming Mexico attacked on U.S. soil.

• Key justification for declaring war.

Abraham Lincoln

• Whig congressman skeptical of Polk’s claims.

• Introduced the Spot Resolutions questioning the war’s legitimacy.

Spot Resolution

• Lincoln demanded the exact spot where American blood was shed.

• Goal: prove whether the attack occurred on U.S. or disputed soil.

Commodore Sloat

• U.S. naval commander.

• Took control of San Francisco in July 1846.

• Raised the U.S. flag and declared California under American control.

General Steaphen Kearny

• Captured Santa Fe, New Mexico without resistance.

• Traveled to California and helped capture Los Angeles (Jan 1847).

Gen Winfield Scott

• Led amphibious landing at Veracruz (March 1847).

• Coordinated Navy + Army assault.

• Oversaw three-day bombardment using Congreve rockets and cannon fire.

• Advanced inland toward Mexico City.

Veracruz

• First major U.S. amphibious landing operation.

• City besieged with rockets and artillery for three days.

• Opened the route for U.S. advance into central Mexico.

Santa Anna

• Mexican general & political leader who returned from exile during the war.

• Commanded Mexican forces at battles including Cerro Gordo and Churubusco.

Cerro Gordo

• Major U.S. victory along route to Mexico City.

• Robert E. Lee scouted mountain paths enabling U.S. flank attack.

• Forced Santa Anna’s forces to retreat.

Battle of Churubusco

• Fought near a monastery south of Mexico City.

• Included San Patricios, Irish Catholic deserters fighting for Mexico.

• Significant step toward the fall of Mexico City.

San Patricios

• Irish Catholic soldiers who defected from the U.S. Army to Mexico.

• Fought fiercely at Churubusco.

• Many were captured and executed by the U.S.

Chapultepec Castle

• Mexican military academy and fort overlooking Mexico City.

• Defended by soldiers and cadets (Niños Héroes).

• Captured by U.S. forces in September 1847.

Cadets/ “Ninos Heroes”

• Young Mexican military cadets who died defending Chapultepec Castle.

• Remembered as national heroes.

Treaty of Guadalupe Hidalgo

• Ended the Mexican-American War (1848).

• U.S. paid $15 million for 525,000 sq. miles of territory.

• Established Rio Grande as the U.S.–Mexico border.