Learn on PengiHistory Alive! - The United States Through IndustrialismChapter 5: An Expanding Nation

Lesson 1: Manifest Destiny and the Growing Nation

In this Grade 8 lesson from History Alive! The United States Through Industrialism, students explore the concept of manifest destiny and how it drove U.S. territorial expansion in the early 1800s. Students examine key acquisitions including the Louisiana Territory, Oregon Country, the Mexican Cession, and the Gadsden Purchase, learning how the nation more than doubled in size between 1803 and 1853 through treaties, settlement, and war. The lesson also challenges students to evaluate whether U.S. expansion across North America was justifiable.

Section 1

Introduction to Manifest Destiny

Key Idea

In the 1840s, a powerful idea swept across the United States. Many Americans came to believe it was their nation's 'manifest destiny' to expand its borders all the way to the Pacific Ocean. They felt it was an obvious and unavoidable mission to spread American ideals and ways of life across the continent.

This belief fueled a strong desire for more land and pushed the nation westward. To achieve this goal, the U.S. government used diplomacy to settle border disputes. For example, leaders from the United States and Great Britain negotiated to officially establish the border of Maine, adding new territory to the growing country.

Section 2

Expansion by Purchase: The Louisiana Territory

Key Idea

American farmers depended on the port of New Orleans to ship their goods. When France's powerful leader, Napoleon, took control of the vast Louisiana Territory in 1800, many Americans feared he would shut down this vital trade route.

However, Napoleon’s plans for an American empire were crushed by a successful slave rebellion in the French colony of Haiti. Led by Toussaint L'Ouverture, the formerly enslaved people defeated French troops, making Napoleon's American ambitions impossible.

Section 3

Expansion by Annexation and Treaty: Texas and Oregon

Key Idea

The idea of expansion dominated the election of 1844. James K. Polk, a surprise candidate, won the presidency by promising to make the United States bigger. Americans saw his victory as a clear signal to claim more territory in the West.

Following through on this promise, Congress annexed Texas as a new state in 1845. This action greatly angered Mexico, which still considered Texas its own territory, and brought the two nations to the brink of war.

Section 4

Causes of the U.S.-Mexican War: The Border Dispute

Key Idea

After the U.S. annexed Texas, a major disagreement erupted over the border. The United States claimed the Rio Grande was the boundary, but Mexico insisted it was the Nueces River. This created a large disputed territory between the two nations.

President James K. Polk sent General Zachary Taylor’s army into this disputed land to assert the American claim. In April 1846, Mexican soldiers crossed the Rio Grande and attacked a U.S. cavalry patrol, sparking the first fight of the conflict.

Lesson overview

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Section 1

Introduction to Manifest Destiny

Key Idea

In the 1840s, a powerful idea swept across the United States. Many Americans came to believe it was their nation's 'manifest destiny' to expand its borders all the way to the Pacific Ocean. They felt it was an obvious and unavoidable mission to spread American ideals and ways of life across the continent.

This belief fueled a strong desire for more land and pushed the nation westward. To achieve this goal, the U.S. government used diplomacy to settle border disputes. For example, leaders from the United States and Great Britain negotiated to officially establish the border of Maine, adding new territory to the growing country.

Section 2

Expansion by Purchase: The Louisiana Territory

Key Idea

American farmers depended on the port of New Orleans to ship their goods. When France's powerful leader, Napoleon, took control of the vast Louisiana Territory in 1800, many Americans feared he would shut down this vital trade route.

However, Napoleon’s plans for an American empire were crushed by a successful slave rebellion in the French colony of Haiti. Led by Toussaint L'Ouverture, the formerly enslaved people defeated French troops, making Napoleon's American ambitions impossible.

Section 3

Expansion by Annexation and Treaty: Texas and Oregon

Key Idea

The idea of expansion dominated the election of 1844. James K. Polk, a surprise candidate, won the presidency by promising to make the United States bigger. Americans saw his victory as a clear signal to claim more territory in the West.

Following through on this promise, Congress annexed Texas as a new state in 1845. This action greatly angered Mexico, which still considered Texas its own territory, and brought the two nations to the brink of war.

Section 4

Causes of the U.S.-Mexican War: The Border Dispute

Key Idea

After the U.S. annexed Texas, a major disagreement erupted over the border. The United States claimed the Rio Grande was the boundary, but Mexico insisted it was the Nueces River. This created a large disputed territory between the two nations.

President James K. Polk sent General Zachary Taylor’s army into this disputed land to assert the American claim. In April 1846, Mexican soldiers crossed the Rio Grande and attacked a U.S. cavalry patrol, sparking the first fight of the conflict.