5.3 Manifest Destiny and the Mexican-American War

LEARNING OBJECTIVE

Explain the causes and effects of the Mexican-American War

INTRODUCTION

• Annexation of Texas led to diplomatic trouble with Mexico. Mexico's anger over annexation and Polk's desire to expand increased the likelihood of war between the US and Mexico.

CONFLICT WITH MEXICO

• Polk sent John Slidell to persuade Mexico to sell California and New Mexico and to settle the Texas border dispute.

• Mexico refused to sell and insisted that the Texas border was at the Nueces River, while the US claimed it was at the Rio Grande.

IMMEDIATE CAUSES OF WAR

• During negotiations, Polk ordered Zachary Taylor to move towards the Rio Grande. Mexican army crossed and attacked US patrols, killing 11 soldiers.

• Polk justified the war by claiming "American blood shed on American soil." Northern Whigs opposed the war, but a majority approved the war resolution.

MILITARY CAMPAIGNS

• The majority of the war was fought by small American armies in Mexican territory.

  • General Stephen Kearney took New Mexico and southern California.

  • John C. Fremont overthrew Mexican rule in northern California, declaring it the Bear Flag Republic.

  • Zachary Taylor's troops drove the Mexican army from Texas into northern Mexico and won the Battle of Buena Vista.

  • Winfield Scott invaded central Mexico, capturing Vera Cruz and Mexico City.

CONSEQUENCES OF THE WAR

• The war was disastrous for Mexico, leading to the Treaty of Guadalupe Hidalgo, which ended the war. Mexico recognized the Rio Grande as Texas's southern border, and the US acquired California and New Mexico for $15 million, assuming responsibility for claims of American citizens against Mexico.

• Opposition arose to the Treaty; Whigs saw it as an attempt to expand slavery, while Southern Democrats wanted to annex all of Mexico.

• The treaty was ultimately ratified in the Senate.

WILMOT PROVISO

• US entry into the war was controversial due to slavery. Congressman David Wilmot proposed a bill to prohibit slavery in the acquired lands, appealing to many Northern lawmakers but was defeated in the Senate.

PRELUDE TO CIVIL WAR

• The acquisition of western lands renewed sectional debate over slavery. Northerners viewed the war as part of a Southern plot, while Southerners recognized they could not depend on Northerners to accept slavery's expansion.