Wars Fought by the United States in the 1800s

Name one war fought by the United States in the 1800s. The United States fought four major wars in the 1800s: the War of 1812, the Mexican-American War (or War with Mexico), the Civil War (or War Between the States), and the Spanish-American War. For the citizenship test, you can name any one of these four wars. Each war shaped American history and territory in important ways.

For the citizenship test, acceptable answers are: War of 1812, Mexican-American War, Civil War, or Spanish-American War.

The Essential Facts

For the citizenship test, memorize at least one of these four wars fought in the 1800s:

War of 1812 (1812-1815):
War against Britain over maritime rights and territorial disputes

Mexican-American War (1846-1848):
War with Mexico that resulted in U.S. gaining southwestern territory

Civil War (1861-1865):
War between Northern states (Union) and Southern states (Confederacy) over slavery and states’ rights

Spanish-American War (1898):
War with Spain that made the U.S. a world power with overseas territories

Any one of these is a correct answer. The Civil War is the most well-known and easiest to remember.

War of 1812 (1812-1815)

The War of 1812 was America’s second war with Britain:

Causes:

• Impressment: Britain forced American sailors to serve in British navy
• Trade Restrictions: Britain interfered with American trade with France
• Native American Conflicts: Britain supported Native American resistance to U.S. expansion in the Northwest
• National Honor: Americans felt Britain treated the U.S. disrespectfully

When: June 1812 – February 1815 (about 2½ years)

Major Events:

• Early Defeats: U.S. invasions of Canada failed
• Naval Victories: U.S. navy won surprising victories over British ships
• Burning of Washington (1814): British burned Washington, D.C., including the White House
• Battle of Baltimore (1814): U.S. defended Baltimore; Francis Scott Key wrote “The Star-Spangled Banner” after watching the bombardment of Fort McHenry
• Battle of New Orleans (1815): Andrew Jackson’s major victory (occurred after peace treaty was signed but before news reached New Orleans)

Outcome:
Treaty of Ghent (December 1814) ended the war. Neither side gained territory. The war was essentially a draw, though Americans celebrated it as a victory because they survived Britain’s attempt to restrain them.

Significance:

• Established U.S. as independent nation that could defend itself
• Created national heroes (Andrew Jackson)
• Inspired national anthem (“The Star-Spangled Banner”)
• Ended British support for Native American resistance in the Northwest
• Led to “Era of Good Feelings” of national unity

Mexican-American War (1846-1848)

The Mexican-American War expanded U.S. territory dramatically:

Causes:

• Texas Annexation: Texas had been independent since 1836 after rebelling against Mexico. The U.S. annexed Texas in 1845. Mexico never recognized Texas independence and viewed annexation as an act of war.
• Border Dispute: The U.S. claimed the Rio Grande as Texas’s southern border; Mexico claimed the Nueces River (further north)
• Manifest Destiny: Many Americans believed the U.S. should expand to the Pacific Ocean
• Polk’s Expansionism: President James K. Polk wanted to acquire California and New Mexico

When: April 1846 – February 1848 (about 2 years)

Major Events:

• Rio Grande Incident: Fighting began in disputed territory between the rivers
• Multiple Campaigns: U.S. forces invaded Mexico from several directions
• Capture of Mexico City (1847): U.S. forces under General Winfield Scott captured Mexico’s capital
• California and Southwest: U.S. forces occupied California and New Mexico territories

Outcome:
Treaty of Guadalupe Hidalgo (1848):

• Mexico ceded about half its territory to the U.S.
• U.S. gained present-day California, Nevada, Utah, most of Arizona and New Mexico, and parts of Colorado and Wyoming
• U.S. paid Mexico $15 million
• Rio Grande became the border

Significance:

• Expanded U.S. territory by about 525,000 square miles
• Fulfilled “Manifest Destiny” of reaching the Pacific
• Added territory that would become rich agricultural and mineral areas (including California Gold Rush)
• Heightened tensions over slavery’s expansion into new territories, contributing to the Civil War
• Established U.S. military capabilities

Controversy:
Many Americans, including Abraham Lincoln, opposed the war as unjust aggression. The war divided Americans between those who supported expansion and those who saw it as immoral conquest.

Civil War (1861-1865)

The Civil War was America’s bloodiest war:

Causes:

• Slavery: The fundamental cause—Southern states wanted to preserve slavery; Northern states increasingly opposed it
• States’ Rights: Southern states claimed the right to leave the Union
• Economic Differences: The industrial North and agricultural South had different economic interests
• Political Power: Conflict over whether new territories would be slave or free states

When: April 1861 – April 1865 (4 years)

The Sides:

• Union (North): 23 states, led by President Abraham Lincoln
• Confederacy (South): 11 states that seceded, led by President Jefferson Davis

Major Events:

• Fort Sumter (April 1861): Confederate attack on this federal fort started the war
• First Bull Run (1861): First major battle; Confederate victory shocked the North
• Antietam (1862): Bloodiest single day in American history; tactical draw but strategic Union victory
• Emancipation Proclamation (1863): Lincoln declared enslaved people in Confederate territory free
• Gettysburg (1863): Major Union victory; turning point of the war
• Vicksburg (1863): Union gained control of Mississippi River
• Sherman’s March (1864): Union forces marched through Georgia and Carolinas
• Appomattox (April 1865): Confederate General Robert E. Lee surrendered to Union General Ulysses S. Grant, effectively ending the war

Casualties:
About 620,000-750,000 soldiers died (more than all other American wars combined). Countless civilians also died.

Outcome:

• Union victory
• Slavery abolished (Thirteenth Amendment, 1865)
• Confederacy dissolved; Southern states rejoined the Union
• Federal government’s supremacy over states established
• Reconstruction period (1865-1877) attempted to integrate freed people into society

Significance:

• Ended slavery
• Preserved the Union
• Established federal government supremacy
• Began process toward racial equality (though genuine equality took much longer)
• Transformed America from loose confederation to unified nation
• Devastated the South economically

The Civil War was the most important event in American history after independence, fundamentally transforming the nation.

Spanish-American War (1898)

The Spanish-American War made the U.S. a world power:

Causes:

• Cuban Rebellion: Cuba was fighting for independence from Spain
• USS Maine: American battleship exploded in Havana harbor (February 1898); newspapers blamed Spain (cause was probably accidental)
• Yellow Journalism: Sensationalist newspapers (especially those of William Randolph Hearst and Joseph Pulitzer) pushed for war
• Humanitarian Concerns: Americans sympathized with Cuban independence
• Imperial Ambitions: Some Americans wanted overseas empire

When: April – August 1898 (about 4 months)

Major Events:

• Declaration of War (April 1898): Congress declared war on Spain
• Battle of Manila Bay (May 1898): Commodore George Dewey destroyed Spanish fleet in the Philippines
• Cuba Campaign: U.S. forces, including Theodore Roosevelt’s “Rough Riders,” fought in Cuba
• Battle of San Juan Hill (July 1898): Famous charge led by Roosevelt
• Spanish Surrender (August 1898): Spain quickly defeated

Outcome:
Treaty of Paris (December 1898):

• Cuba gained independence
• U.S. acquired Puerto Rico, Guam, and the Philippines
• U.S. paid Spain $20 million for the Philippines

Significance:

• Made U.S. a colonial power with overseas territories
• Established U.S. as world power
• Marked end of Spanish colonial empire
• Led to Philippine-American War (1899-1902) when Filipinos fought American occupation
• Made Theodore Roosevelt a national hero; he became president in 1901
• Demonstrated American military power

Controversy:
Anti-imperialists, including Mark Twain, opposed acquiring colonies. They argued it violated American principles of self-government and freedom. The debate over imperialism divided Americans.

Why These Wars Mattered

Each war shaped America:

War of 1812:

• Established U.S. independence and respect
• Created national identity and pride
• Ended British interference in American affairs

Mexican-American War:

• Expanded U.S. to Pacific coast
• Acquired territory that became wealthy, populous states
• Heightened tensions leading to Civil War

Civil War:

• Ended slavery
• Preserved the Union
• Transformed America into modern nation

Spanish-American War:

• Made U.S. a world power
• Acquired overseas territories
• Demonstrated American military strength

Together, these wars expanded U.S. territory from the Atlantic coast to the Pacific Ocean and beyond, ended slavery, and established America as a world power.

Other 1800s Conflicts

The U.S. fought other conflicts in the 1800s not usually counted as “wars”:

Indian Wars:
Numerous conflicts with Native American tribes throughout the century as the U.S. expanded westward. These were technically wars but are often not counted as major wars.

Barbary Wars (1801-1805, 1815):
Conflicts with North African states over piracy. The first occurred in the early 1800s.

Various Interventions:
Small military actions in Latin America and Asia.

For the citizenship test, stick to the four major wars: War of 1812, Mexican-American War, Civil War, and Spanish-American War.

How to Remember

Memory tips for the citizenship test:

Easiest to Remember:
The Civil War (1861-1865). This is the most famous and most important. If you remember only one, remember the Civil War.

Chronological Order:

1. War of 1812 (1812-1815)
2. Mexican-American War (1846-1848)
3. Civil War (1861-1865)
4. Spanish-American War (1898)

Key Words:

• War of 1812: Britain, “Star-Spangled Banner”
• Mexican-American: Mexico, gained California
• Civil War: North vs. South, slavery
• Spanish-American: Spain, gained Philippines

Connections That Matter

Understanding 1800s wars connects to American territorial expansion. The Mexican-American War and earlier conflicts with Britain and Native Americans expanded U.S. territory from coast to coast.

These wars relate to slavery and its abolition. The Mexican-American War heightened tensions over slavery’s expansion. The Civil War ended slavery. Both shaped America’s path toward equality.

The wars also connect to America becoming a world power. The Spanish-American War marked America’s emergence onto the world stage as an imperial power with global interests.

For more on these wars, see our articles on the Civil War, Emancipation Proclamation, and American expansion in the uscis-questions category. To understand territorial growth, read about how America expanded. To learn about individual wars, explore detailed histories of each conflict.

Top 10 Frequently Asked Questions

Which war should I memorize for the test?
The Civil War is easiest to remember and most important. If you know only one, know the Civil War (1861-1865), fought between North and South over slavery.

Do I need to know dates?
Not for the test, but knowing the century (1800s) helps. The Civil War (1861-1865) is the most important date to know.

What if I name a war from another century?
The question asks for 1800s wars. Revolutionary War (1775-1783) was in the 1700s. World War I (1914-1918) and World War II (1939-1945) were in the 1900s. Don’t name these for 1800s question.

Was the War of 1812 in the 1800s?
Yes. 1812 is in the 1800s (19th century). The century name is confusing—the 1800s are the 19th century, the 1900s are the 20th century, etc.

Which war was most important?
The Civil War. It ended slavery, preserved the Union, and transformed America fundamentally.

Did the U.S. win all these wars?
Mostly. War of 1812 was a draw. The U.S. won the Mexican-American War, Civil War (Union victory), and Spanish-American War decisively.

Why are Indian Wars not listed?
They’re usually not counted as major wars, though they were numerous and significant. For the citizenship test, focus on the four major wars listed.

What was the bloodiest war?
The Civil War. About 620,000-750,000 Americans died—more than all other American wars combined.

Did all Americans support these wars?
No. Each war had opponents. The Mexican-American War and Spanish-American War were especially controversial.

What should I memorize for the citizenship test?
Memorize at least one war: Civil War (easiest), War of 1812, Mexican-American War, or Spanish-American War. Any one is a correct answer. Know the Civil War fought between North and South over slavery. This is sufficient.