Wars Fought by the United States in the 1900s

USCIS Questions Reading Time: 8 minutes

Name one war fought by the United States in the 1900s: World War I, World War II, Korean War, Vietnam War, or Persian Gulf War.

Name one war fought by the United States in the 1900s. The United States fought several major wars in the 1900s (20th century): World War I, World War II, Korean War, Vietnam War, and (Persian) Gulf War. For the citizenship test, you can name any one of these wars. Each war shaped American history and America’s role in the world in important ways.

For the citizenship test, acceptable answers are: World War I, World War II, Korean War, Vietnam War, or (Persian) Gulf War.

The Essential Facts

For the citizenship test, memorize at least one of these five wars fought in the 1900s:

World War I (1917-1918):
U.S. joined Allied Powers fighting Germany and Austria-Hungary in Europe

World War II (1941-1945):
U.S. fought Germany, Italy, and Japan after Pearl Harbor attack

Korean War (1950-1953):
U.S. fought to defend South Korea from North Korean and Chinese invasion

Vietnam War (1964-1975):
U.S. fought to prevent communist takeover of South Vietnam

Persian Gulf War (1991):
U.S. led coalition to liberate Kuwait from Iraqi invasion

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

World War I (1917-1918)

America’s entry into “The Great War”:

Dates: U.S. involvement April 1917 – November 1918

Why the U.S. Entered:

  • German submarine attacks on American ships
  • Zimmermann Telegram (Germany tried to ally with Mexico against the U.S.)
  • Economic ties to Britain and France
  • Desire to make the world “safe for democracy” (President Wilson’s phrase)

U.S. Role:

  • Sent about 2 million soldiers to Europe (“doughboys”)
  • Tipped the balance in favor of Allies (Britain, France, Russia, Italy)
  • Fresh American troops helped defeat exhausted German forces

Result:

  • Allied victory; Germany and Austria-Hungary defeated
  • Treaty of Versailles (1919) ended the war
  • League of Nations created (though U.S. never joined)
  • About 116,000 American deaths

Significance:

  • First time U.S. sent large army to fight in Europe
  • Made U.S. a world power
  • Set stage for World War II (harsh treaty terms led to German resentment)

World War II (1941-1945)

America’s largest and most important war:

Dates: U.S. involvement December 1941 – August 1945

Why the U.S. Entered:

  • Japanese attack on Pearl Harbor (December 7, 1941)
  • Germany and Italy declared war on U.S. after Pearl Harbor
  • U.S. had been helping Britain and Soviet Union before officially entering

The Enemy:

  • Axis Powers: Germany (led by Adolf Hitler), Japan (led by Emperor Hirohito), Italy (led by Benito Mussolini)
  • Allied Powers: United States, Britain, Soviet Union, China, France, and others

Major Events:

  • D-Day (June 6, 1944): Allied invasion of Nazi-occupied France
  • Battle of the Bulge (1944-1945): Last major German offensive
  • Island Hopping Campaign: U.S. forces fought across Pacific toward Japan
  • Atomic Bombs (August 1945): U.S. dropped atomic bombs on Hiroshima and Nagasaki, Japan

Result:

  • Allied victory
  • Germany surrendered May 8, 1945 (V-E Day)
  • Japan surrendered August 15, 1945 (V-J Day)
  • About 405,000 American deaths (more than any other U.S. war except Civil War)

Significance:

  • Defeated Nazi Germany and Imperial Japan
  • Ended the Holocaust (Nazi genocide of 6 million Jews)
  • Made U.S. a superpower
  • Led to Cold War with Soviet Union
  • United Nations created to prevent future wars

World War II was the most important war of the 20th century.

Korean War (1950-1953)

The first major conflict of the Cold War:

Dates: June 1950 – July 1953

Why the U.S. Fought:

  • North Korea (communist, supported by Soviet Union and China) invaded South Korea (non-communist, supported by U.S.)
  • U.S. wanted to stop spread of communism (“containment”)
  • United Nations authorized military action to defend South Korea

What Happened:

  • North Korean forces nearly conquered entire South Korea
  • U.S. and UN forces (led by General Douglas MacArthur) pushed North Koreans back
  • China entered war to support North Korea
  • War settled into stalemate near original border (38th parallel)

Result:

  • Armistice (ceasefire) signed July 27, 1953
  • Korea remained divided at roughly the same border
  • About 36,000 American deaths
  • Technically still at war (only armistice, not peace treaty)

Significance:

  • First limited war (U.S. did not use full power to win decisively)
  • Demonstrated U.S. commitment to containing communism
  • Korea remains divided today (North Korea vs. South Korea)
  • Set precedent for U.S. military involvement in Asia

Vietnam War (1964-1975)

America’s longest and most controversial war of the 20th century:

Dates: Major U.S. involvement 1964-1973; war ended 1975

Why the U.S. Fought:

  • North Vietnam (communist) fought South Vietnam (non-communist)
  • U.S. wanted to prevent communist takeover (“domino theory”—if Vietnam fell, other countries would too)
  • Started with military advisors, escalated to major combat forces

What Happened:

  • U.S. sent over 500,000 troops at peak (1968)
  • Guerrilla warfare made it difficult to achieve victory
  • Tet Offensive (1968) shocked Americans and turned public opinion against war
  • Anti-war protests grew in U.S.
  • U.S. gradually withdrew forces (1969-1973)

Result:

  • Paris Peace Accords (1973) ended U.S. involvement
  • North Vietnam conquered South Vietnam in 1975
  • Communist victory; Vietnam united under communist government
  • About 58,000 American deaths

Significance:

  • First war U.S. clearly lost
  • Deeply divided American society
  • Led to War Powers Act (1973) limiting presidential war powers
  • Made Americans skeptical of military interventions
  • Showed limits of U.S. military power

The Vietnam War was traumatic for America and remains controversial.

Persian Gulf War (1991)

Brief war that demonstrated U.S. military dominance:

Dates: January-February 1991 (about 6 weeks of combat)

Why the U.S. Fought:

  • Iraq (led by Saddam Hussein) invaded and occupied Kuwait (August 1990)
  • U.S. led international coalition to liberate Kuwait
  • Protect oil supplies from Persian Gulf
  • Enforce United Nations resolutions

What Happened:

  • Massive air campaign (Operation Desert Storm) destroyed Iraqi forces
  • Ground war lasted only 100 hours
  • Iraqi forces driven from Kuwait
  • Coalition stopped short of invading Iraq or removing Saddam Hussein

Result:

  • Kuwait liberated
  • Iraqi forces defeated decisively
  • About 150 American deaths (combat)
  • Ceasefire, but Saddam remained in power

Significance:

  • Demonstrated U.S. military superiority after Cold War
  • Showed effectiveness of precision weapons and air power
  • Quick, decisive victory
  • Left unfinished business with Iraq (led to 2003 Iraq War)
  • Made U.S. dominant military power

How to Remember

Memory tips for the citizenship test:

Easiest to Remember:
World War II (1941-1945). This is the most famous and most important. If you remember only one, remember World War II.

Chronological Order:

  1. World War I (1917-1918)
  2. World War II (1941-1945)
  3. Korean War (1950-1953)
  4. Vietnam War (1964-1975)
  5. Persian Gulf War (1991)

Key Words:

  • World War I: Germany, “The Great War”
  • World War II: Hitler, Pearl Harbor, D-Day, atomic bomb
  • Korean War: North Korea invaded South Korea, 38th parallel
  • Vietnam War: Longest war, lost, guerrilla warfare
  • Persian Gulf War: Kuwait, Saddam Hussein, Desert Storm

Other 1900s Conflicts

The U.S. was involved in other military actions in the 1900s:

Spanish-American War (1898):
Technically fought in the 1800s (1898), though some effects continued into 1900s

Philippine-American War (1899-1902):
After Spanish-American War, Filipinos fought U.S. occupation

Panama Intervention (1989):
Small operation to remove Panamanian dictator Manuel Noriega

Somalia (1992-1993):
Humanitarian intervention that ended badly

Bosnia and Kosovo (1990s):
U.S. involved in peacekeeping and air strikes

For the citizenship test, stick to the five major wars: World War I, World War II, Korean War, Vietnam War, and Persian Gulf War.

Comparison of the Five Wars

Size:

  • Largest: World War II (16 million Americans served)
  • Smallest: Persian Gulf War (697,000 served)

Casualties:

  • Most deaths: World War II (405,000)
  • Fewest deaths: Persian Gulf War (about 150 combat deaths)

Duration (U.S. involvement):

  • Longest: Vietnam War (about 11 years)
  • Shortest: Persian Gulf War (6 weeks)

Outcome:

  • Clear victories: World War I, World War II, Persian Gulf War
  • Stalemate: Korean War (divided Korea remains)
  • Defeat: Vietnam War (communist victory)

Impact:

  • Most significant: World War II (defeated fascism, made U.S. superpower)
  • Most controversial: Vietnam War (divided nation, first clear defeat)

Why These Wars Mattered

Each war shaped America:

World War I:

  • Made U.S. a world power
  • Ended American isolationism
  • Set stage for World War II

World War II:

  • Defeated fascism
  • Made U.S. a superpower
  • Created modern world order

Korean War:

  • First limited war
  • Contained communism
  • Korea remains divided

Vietnam War:

  • Showed limits of U.S. power
  • Changed how Americans view military intervention
  • Led to reforms in how U.S. enters wars

Persian Gulf War:

  • Demonstrated U.S. military dominance
  • Protected oil supplies
  • Left unfinished business in Iraq

Connections to Other Topics

Understanding 1900s wars connects to:

American foreign policy: These wars shaped U.S. role as world power

Presidential powers: Wars led to debates about presidential war authority

Civil rights: World War II led to civil rights movement; Vietnam War era saw social changes

Technology: Wars drove technological advancement

For more information, see related articles in the uscis-questions category on presidents who led during these wars, American foreign policy, and military history.

Top 10 Frequently Asked Questions

Which war should I memorize for the test?
World War II is easiest to remember and most important. If you know only one, know World War II (1941-1945), fought against Germany and Japan after Pearl Harbor.

Do I need to know dates?
Not for the test, but knowing the century (1900s) helps. World War II (1941-1945) is the most important date to know.

What if I name a war from another century?
The question asks for 1900s wars. The Revolutionary War (1775-1783), War of 1812 (1812-1815), Mexican-American War (1846-1848), and Civil War (1861-1865) were in earlier centuries. Afghanistan and Iraq wars (2001 and 2003) began in the 2000s. Don’t name these for 1900s question.

Was World War II the biggest war?
Yes, it was the largest war in human history. Over 60 million people died worldwide. About 16 million Americans served.

Did the U.S. win all these wars?
No. The U.S. won World War I, World War II, and Persian Gulf War. Korean War was a stalemate. Vietnam War was a defeat.

Why is Vietnam War important if the U.S. lost?
It was America’s longest war and first clear defeat. It profoundly affected American society and changed how Americans view military intervention.

What was the Gulf War about?
Iraq invaded Kuwait. The U.S. led a coalition to liberate Kuwait. It was about defending a small country and protecting oil supplies.

How many Americans died in these wars?
Approximately: World War II (405,000), Vietnam War (58,000), World War I (116,000), Korean War (36,000), Persian Gulf War (150 combat deaths).

Are any of these wars still going on?
The Korean War technically never ended—only an armistice (ceasefire), not a peace treaty. Korea remains divided. The others ended.

What should I memorize for the citizenship test?
Memorize at least one war: World War II (easiest), World War I, Korean War, Vietnam War, or Persian Gulf War. Any one is a correct answer. Know World War II was fought against Germany and Japan after Pearl Harbor (1941-1945). This is sufficient for the test.

Similar Posts