The Mexican-American War On March 2, 1845, The U.S. Congress voted to annex Texas and admit it as a state. On March 4, James K. Polk was inaugurated as president. Two days after Polk took office, the Mexican ambassador left Washington in protest over the annexation of Texas. Polk dispatched John Slidell to Mexico to offer a settlement. The Mexicans expelled Slidell after he insisted on the Rio Grande border of Texas and offered money for California and New Mexico. Polk took a unilateral course by dispatching U.S. troops under Gen. Zachary Taylor to the Rio Grande.

Declaration of War Slidell arrived back in Washington on the morning of May 9. That very night, word arrived that U.S. troops had been attacked north of the Rio Grande. “American blood had been shed on American soil,” Polk told Congress and both houses overwhelmingly approved his war declaration. Polk’s initial support in Congress was short lived. Northerners, especially Whigs, opposed the war in large numbers. Former President J.Q. Adams denounced the war. An obscure first-term Congressman from Illinois named Abraham Lincoln repeatedly introduced so-called “spot resolutions” in the House attempting to undermine and embarrass Polk.

Both the U.S. and Mexico were ill prepared for war. The U.S. Army numbered only 7,000 and the larger Mexican army (32,000) possessed badly outdated weapons and was poorly disciplined. Polk was concerned that the two leading generals in the U.S. Army would use their success in war to strengthen the Whig party. He was correct. General Zachary Taylor would be the Whig nominee for president in 1848 (he won) and General Winfield Scott in 1852 (he lost).

Zachary Taylor: several victories in northern Mexico including Monterey. Winfield Scott: landed at Vera Cruz and took Mexico City. Stephen Kearny: marched from Fort Leavenworth (now Kansas) to Santa Fe and took New Mexico relatively unopposed. John C. Fremont: initiated the “Bear Flag Revolt” in California.

The Treaty of Guadalupe-Hidalgo February 2, Mexico gave up all claims to Texas north of the Rio Grande. 2. Mexico ceded California and New Mexico to the U.S. 3. The U.S. would pay Mexico $15 million. 4. The U.S. would assume all claims of U.S. citizens against Mexico up to $3.25 million.

The Mexican-American War