The Age of Expansionism
AP US History
• Territorial expansion
• Commercial development
• Technological progress
• “Young America” – spirit of the
time: positive attitude toward
market economy and industrial
growth, a more aggressive foreign
policy, and a celebration of virtues
Manifest Destiny
• Believe that God
had ordained
expansion across
the continent
• Led to diplomatic
with Britain and
Land Acquisitions
• Webster-Ashburton Treaty, 1842
• Annexation of Texas, 1845
• Oregon dispute settled, 1846
• Treaty of Guadalupe Hidalgo, 1848
• Gadsden Purchase, 1853
Texas Independence
• Mexico encouraged American settlement in Texas in the
• Led to problems by 1830s (slavery question, role of
Catholic Church), and Mexico, under Santa Anna,
moved to quell independence-minded Texans
• Texans revolted in 1835-1836. Rallying behind losses at
the Alamo and Goliad, Texans defeated Mexico at San
• General Sam Houston became the first president of the
“Lone Star Republic,” independent until 1845
Texas Annexation
• Jackson, president at time of
Independence, steered clear of
annexation debate
• President Tyler push for annexation, but
Senate voted down the treaty
• President Polk successfully campaigned
for the annexation of Texas, official in
The Mexican-American War
• Mexico refused to recognize Rio Grande
as Texas border, and refused to sell
land to U.S.
• Under Polk’s aggressive expansionist
policies, the U.S. declared war on
Mexico in 1846
• Under Taylor, Kearney, Fremont, and
Scott, the U.S. military quickly
Treaty of Guadalupe Hidalgo, 1848
• Mexican cession – most of present day New
Mexico, Arizona and California for $15 million
• Recognition of Rio Grande as border
• U.S. government assumes American claims
against Mexico
• Gasdsen Purchase, 1853, gave U.S. southern
most parts of New Mexico and Arizona
(potential southern railroad route)
Internal Expansion
• By the 1830s, Americans moved west,
attracted by adventure, prospect of
financial gain, and (for the Mormons)
religious freedom
• Americans traveled west on the Santa
Fe Trail (1820s) and the Oregon Trail
• Discovery of gold in California in 1848
led to mass movement westward
Innovation and Expansion
• Telegraphs and railroads aided internal
expansion (by the 1840s, railroads
replaced canals as primary means of
internal transport)
• Railroad and manufacturing led to boom
in industry, more jobs, and more
• Agricultural innovations eased farming
and led to more settlement
• McCormick’s reaper
• Deere’s plow
Native Americans on the
• In 1834, the national government
passed the Indian Intercourse Act,
prohibiting settlers from going on
Indian land.
• Settlers (and the government) ignored
this agreement as economic prospects
expanded out west
• Government changed their policies
several times in the period beyond the
Civil War, stay tuned

Lecture: The Age of Expansionism 1830-1860