World Wars and the American Century: 1914–1945

Posted on Dec 6, 2025 in History

World War I: Causes, Conflict, and Consequences

The Four Main Causes of WWI

Explain the significance and key people or parties involved/impacted:

  1. Militarism, Alliances, Imperialism, Nationalism (MAIN)

    • Nationalism: Pride in one’s national identity. Cultures desired self-determination without foreign interference.
    • Imperialism: The process of turning colonies into “empires,” leading to intense competition between nations.
    • Militarism: The development of stronger armed forces and weapons in competition with rivals.
    • Alliances: The formation of complex defense treaties.
      • Triple Entente: Britain, France, and Russia.
      • Triple Alliance: Germany, Austria-Hungary, and Italy (Note: Italy later switched sides).

The United States Enters the War

The US joined the war primarily due to German actions violating neutrality and threatening American lives:

  • Sinking of the British Passenger Ship Lusitania: A German U-boat sank the ship, killing 1,198 people, including 128 Americans. Germany justified the attack because the ship was carrying war supplies.
  • Violation of the Sussex Pledge: The US threatened Germany if unrestricted submarine attacks did not stop. Germany violated this pledge.
  • The Zimmermann Note: The German Foreign Minister sent a telegram to Mexico proposing a military alliance against the US. If Germany won, Mexico would regain lost territory (Texas, New Mexico, Arizona).

Key Events and Realities of WWI

The Sinking of the Lusitania

A German U-Boat killed approximately 1,200 passengers, including 128 Americans. This event was a major factor in turning American public opinion against Germany. Germany temporarily ended submarine warfare afterward.

New Realities of Trench Warfare

Soldiers faced horrific conditions, including:

  • Lice, polluted water, and dysentery.
  • The constant smell of poison gas and decaying bodies.
  • Trench foot (toes started to rot) and severe gum/mouth infections.

On the home front, the Food Administration asked citizens to conserve food for soldiers, and women took on “men’s work” in factories.

Wartime Measures and Legislation (1917)

The US Government took several measures to prepare for and manage the war effort:

  • Selective Service Act: Required men to register for military service (a draft).
  • War Industries Board (WIB): Encouraged mass production techniques to increase efficiency and standardize products.
  • War Bonds: A method for the government to borrow money from citizens to finance the war, repaying them later with interest.
  • Sedition Act: Made disloyalty to the USA or speaking out against the government during the war period a crime.
  • Espionage Act: Prohibited interference with military operations or recruitment.
  • Committee of Public Information (CPI): A propaganda agency created to influence public opinion in favor of the war effort.

WWI Peace Efforts and Treaties

Wilson’s Fourteen Point Plan

President Woodrow Wilson proposed the Fourteen Point Plan in January 1918 to maintain peace. It was divided into three main sections:

  1. First 5 Points: Focused on preventing future wars (e.g., freedom of the seas, reduction of arms).
  2. Next 8 Points: Focused on “self-determination,” meaning nations should not be ruled by outside groups, leading to boundary changes.
  3. Last Point: Proposed the “League of Nations,” an international body for discussing struggles and resolving conflicts without resorting to war.

The Treaty of Versailles

Signed on June 28, 1919, the Treaty of Versailles was a series of compromises intended to formally end the war. Representatives from Britain, France, the United States, and Italy were invited; Germany was not. The treaty required approval by the US Senate, which ultimately rejected it.

Post-WWI America: The Roaring Twenties

Social and Political Controversies

  • Significance of Sacco and Vanzetti: Nicola Sacco and Bartolomeo Vanzetti were Italian anarchists convicted and executed for murder and robbery in 1927, despite little conclusive evidence against them. Their case highlighted anti-immigrant and anti-radical sentiment.
  • Radical Immigrants: People who sought extreme political or social changes, often associated with anarchism or communism during the Red Scare.
  • 1920s Controversies:
    • Women in Manufacturing: Women had an important influence on industrial production, which contributed to the passage of the 19th Amendment (suffrage).
    • Consumer Buying Practices: Demand for raw materials and consumerism was initially low because many people had low incomes.
  • The Harlem Renaissance: A period of cultural development and impact, particularly through the work of African American artists, writers, and musicians (like Jazz), reflecting racial and economic philosophies.
  • Hollywood: Movies featured women serving during wartime and provided conventional pieces of theater that offered perspectives on life during the war and the 1920s.
  • The Prohibition (18th Amendment): Brought about by religious and moral ideas, as well as the belief that it was unpatriotic to use wheat and corn for alcohol production when soldiers overseas needed food supplies. It caused a rise in organized crime and illegal speakeasies.

Key African American Leaders

  • Marcus Garvey: Founder of the “Back to Africa” movement, promoting black pride and economic independence.
  • W.E.B. DuBois: A black activist, writer, sociologist, and teacher whose work is considered foundational in African American studies.
  • Booker T. Washington: An American educator born into slavery who became a leading intellectual of the late 19th and early 20th centuries, advocating for vocational education.

International Diplomacy Post-WWI

Three major efforts aimed at maintaining global peace and stability:

League of Nations
An international organization designed to hold conferences and resolve disputes without resorting to war.
Kellogg-Briand Pact (1928)
An agreement that attempted to outlaw war as an instrument of national policy.
Washington Naval Conference (1921–1922)
A meeting aimed at reducing the size of the navies of the world’s major powers.

The Great Depression and the New Deal

Long-Term Effects and Impacts

  • Great Depression: Characterized by mass unemployment, homelessness, and the collapse of international trade.
  • Shantytowns: Deprived areas on the outskirts of towns consisting of large numbers of makeshift dwellings (often nicknamed “Hoovervilles”).
  • Dust Bowl: A region of the drought-stricken Southern Plains that suffered from severe dust storms due to poor farming practices and high winds.

Major Government Programs of the New Deal

The New Deal was a series of programs and reforms implemented by President Franklin D. Roosevelt to combat the Great Depression:

  • Agricultural Adjustment Administration (AAA): Restored agricultural prosperity by reducing crop production and paying farmers subsidies.
  • Civilian Conservation Corps (CCC): Relieved unemployment by providing national conservation work for young men.
  • National Recovery Administration (NRA): Stimulated business recovery through establishing fair practice codes and minimum wages (later ruled unconstitutional).
  • Public Works Administration (PWA): Increased purchasing power and reduced unemployment through the construction of highways and public buildings.

World War II: Conflict and Aftermath

Causes of WWII

The rise of global tensions leading to the second world conflict:

  • The punitive nature of the Treaty of Versailles.
  • The rise of Italian Fascism (Mussolini).
  • The rise of Hitler and the Nazi Party in Germany.
  • The spread of Anti-Communism.
  • Renewed Militarism and Nationalism.
  • U.S. Isolationism, which limited intervention in early conflicts.

US Entry into WWII

The US joined the war after the attack on Pearl Harbor, fighting primarily against the Japanese Empire and the Axis Powers.

The Attack on Pearl Harbor

On December 7, 1941, Japanese planes attacked the US naval base in Hawaii territory through bombing, killing 2,403 Americans and destroying several American battleships. This attack was a response to US provocations, including economic sanctions.

Key Wartime Events and Tactics

  • Japanese-American Internment Camps: Forced relocation and incarceration of people of Japanese descent in concentration camps. This is considered one of the most atrocious violations of civil liberties in American history.
  • Carpet Bombing: A technique developed for planes to scatter a large number of bombs over a wide area, destroying everything in the path.
  • Atomic Bombings (Hiroshima and Nagasaki): An American B-29 dropped the first atomic bomb on Hiroshima (August 6, 1945). Three days later, a second A-bomb was dropped on Nagasaki, killing around 40,000 people instantly, leading to Japan’s surrender. The use of the atomic bomb was authorized by President Harry S. Truman.
  • Manhattan Project: The code name for the development of the Atomic Bomb. It consisted of many Allied scientists, including German and Italian refugees, working to split the atom and create the world’s first nuclear weapon. The project leader was Dr. Robert Oppenheimer.
  • Operation Sea Lion: Hitler’s (Germany’s) invasion plan for Great Britain, which relied solely on air bombings to force them to surrender.
  • Stalingrad: The main reason the German military push stalled in Stalingrad was due to the harsh Russian winter, often nicknamed “General Winter.”
  • Kamikaze: A Japanese pilot who takes off in his fighter plane with no intention of landing. They unload all ammunition and then crash the aircraft into a high-value target.

The Holocaust and Concentration Camps

  • Main Source of Execution: Gas Chambers.
  • Hitler’s Targets for Concentration Camps:
    • Jews
    • Homosexuals
    • Anyone with any type of disability
    • Slavs
    • Gypsies
    • Polish Citizens or anyone who spoke Polish

Post-WWII Global Role

  • US Role Around the World: The USA was still recovering from the impacts of the Great Depression and unemployment, which had a negative, yet significant, impact on their economy. Despite this, the US emerged as a global superpower.
  • Nuremberg Trials: War crimes tribunals held for German officers accused of atrocities during the war.
  • United Nations: An international organization formed after WWII to promote international peace, security, and cooperation.

Key Figures, Alliances, and Terms

WWI Key Figures and Terms

Francis Ferdinand
Archduke of Austria-Hungary whose assassination by Serb nationalists on June 28, 1914, triggered WWI.
William II
The German Emperor during WWI.
Alsace-Lorraine
French region lost to German states in 1871, a source of French resentment.
Militarism
The glorification of the military.
Western Front
The battle front between the Allies and Central Powers in western Europe during WWI.
Casualty
A killed, wounded, or missing soldier.
Contraband
Supplies captured from an enemy during wartime.
U-boat
German submarine.
Lusitania
British passenger ship sunk by a German U-boat during WWI.
Zimmermann Note
A telegram in which the German foreign minister proposed an alliance with Mexico against the United States.

WWI Alliances

  • The Allied Powers: Included Britain, France, Russia, and Serbia (later joined by the US and Italy).
  • The Central Powers: Included Germany and Austria-Hungary.

WWII Key Figures and Terms

Axis Powers
The alliance formed by Japan, Italy, and Germany.
Allies
Great Britain, France, the Soviet Union, and the United States.
The Big 3
The nickname given to the leaders: Churchill (UK), Stalin (USSR), and Roosevelt (US).
Appeasement
Giving in to the demands of an aggressor in order to keep the peace.
Erwin Rommel
Hitler’s military leader, nicknamed the “Desert Fox.”
Joseph Stalin
Leader of the Soviet Union.
Pacifism
Opposition to all war; the belief that war is never justified.

Post-WWI Government Systems in Europe

  • Democracy: Great Britain and France.
  • Fascism: Germany and Italy.
  • Communism: Soviet Union.