Mexican-American War Lesson Plan

Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

Using this lesson plan on the Mexican-American War, your students will not only learn about the events of the war and its conduct, but also how victory in the war started new questions about slavery.

Learning Objectives

In this lesson students will be able to:

  • Identify the causes of the Mexican-American War.
  • Analyze the causes for instability in Texas between Mexican independence and the Mexican-American War.


30 minutes, then 40 minutes for activity

Curriculum Standards


Determine the central ideas or information of a primary or secondary source; provide an accurate summary of how key events or ideas develop over the course of the text.


  • First, watch the video The Mexican-American War, Treaty of Guadalupe Hidalgo, & the Wilmot Proviso in class, pausing for the following discussion prompts:
  • 1:01 - Remind students of the story of the Alamo and the fact that Texas was independent for some years. How was Texas more like the United States? How was Texas more like Mexico?
  • 4:18 - Why do you think that Polk was so anxious to avoid Mexico selling land to Britain? What does this say about fears about Britain?
  • 7:29 - Drawing back to the Missouri Compromise and other earlier legislation on slavery, how might victory in the Mexican-American War have changed the outlook of slavery in the United States?


Split your class into small groups of 4-5 students each. Ask each group to take an aspect of the Mexican-American War, as listed below, and discuss it in reference to the following concepts dealing with two crucial questions of American history during this period:

  • Manifest Destiny
  • Slavery.

Here are some sample concepts dealing with Manifest Destiny:

  • Preventing sale of modern-day California, Arizona, Nevada, New Mexico, and Colorado to the British
  • Protecting the rights of Americans living in Mexican Texas (especially debts)
  • Not taking over the rest of Mexico (remember that the Americans had conquered Mexico City)

Here are some sample concepts dealing with slavery:

  • Popular Sovereignty seemed to be a perfect solution. Drawing on the divisiveness of certain issues we face today, how can you see this as being doomed from the start?
  • The Wilmot Proviso could have helped the majority of Southerners as it was targeted at only forbidding rich plantation owners to arrive with their slaves. Was Calhoun helping all Southerners or just the rich?

After 10 minutes of discussion, bring the class back together and have each group present its opinions. From there, discuss as a class how these two concepts of slavery and Manifest Destiny were linked and how the slavery question had to first be resolved for Manifest Destiny to be completed in practice.


  • A sizable chunk of the United States was annexed as a result of the Mexican-American war. Ask students to discuss how things might have been different had the war went the other way.
  • Relate the idea of Manifest Destiny to the execution of the war.

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