Mexican-American War 1846-1848

Causes of the War 1) Election of James K. Polk (1844) Democratic President who promised to annex Texas (Mexico) and Oregon (GB) and buy California (Mexico). Popular platform that expanded the country but maintained the balance of power between slave and free states. 2) Question of extending slavery Northern and Southern states were very concerned about either side gaining another state, more representatives, and more power in Congress. 3) Argument over Oregon and California Popular opinion was with Polk, but he found middle ground and agreed to split the Oregon territory with GB (1846).

Causes of the War (cont.) 4) Annexation of Texas Previous President (Tyler) pushed through the annexation of Texas in 1845, which Mexico still believed was theirs. 5) Border Dispute and Failed Negotiation Complications over where Texas’s southern border was (Nueces River or Rio Grande River). Polk sends John Slidell down to Mexico City to negotiate with Mexican President Jose Joaquin Herrera, but Herrera refused to meet with him.

Nueces (Mexico) vs. Rio Grande (U.S.A.)

War Begins President Polk ordered American forces under Gen. Zachary Taylor to cross south of the Nueces River (disputed territory). May 9, 1846: Understandably, Mexican soldiers fired upon the invading Americans, and Polk now had his case for war. “American blood has been shed on American soil!” (Polk) May 13, 1846: Congress declared war on Mexico.

War Increased the size of the U.S. Army by adding 73,000 volunteers (asked for 50,000). Three-prong attack that ended in a coordinated assault on Mexico City. Gulf of Mexico; New Mexico; California. Attack through California was aided when Californian citizens rebelled against Mexico in the Bear Flag Revolt. A few weeks later, the Bear Flag Republic was annexed by the U.S.

Campaigns of the War

Final Phases Mexico was defeated on the battlefield, but its military leadership refused surrender. March 1847: Polk launched troops at Veracruz under the command of Winfield Scott. Polk feared Zachary Taylor as a political rival, so he relieved him of command and gave it to Scott. Sept. 14, 1847: American forces sack the Mexican capital.

American Forces Occupying Mexico City

Treaty of Guadelupe-Hidalgo Feb. 2, 1848: Mexico’s leaders agree to a peace treaty. Mexico gave up over 500,000 square miles of territory to the U.S. (CA, UT, NV, NM, AZ, CO, WY). Southern border of Texas was the Rio Grande. U.S. paid Mexico $15 million and assumed $3.25 million of debt Mexico owed American citizens for a grand total of $18.25 million.

Famous Generals on the Same Side . . Robert E. Lee Ulysses S. Grant