Skip to Main Content
It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.

World War I: Causes, Themes, Legacy

WWI Triggers - The "Causes"

(1912-1913)
The Balkan Wars preceded World War I, but understanding the context of the Balkan Wars helps to understand the outset of World War I

Wounded Bulgarian soldiers during the Balkan campaigns 1912-13.
Wounded Bulgarian Soldiers During The Balkan Campaigns 1912-13. Fine Art. Encyclopædia Britannica Image Quest

Bosnian student Gavrilo Princip, the suspected assassin of Archduke Franz Ferdinand, is hustled into custody in Sarajevo in 1914. Because of Princip's swift capture, he was unable to swallow the cyanide pill he had tucked in his pocket.
"capture of Archduke Ferdinand's killer." Image. The Illustrated London News Picture Library. World History: The Modern Era. ABC-CLIO, 2011. Web. 6 Nov. 2011.

Background of Schlieffen Plan

In Brief
In 1904, Britain, France, and Russia formed an alliance called the "Triple Entente" as a means to protect their countries from the might of the "Triple Alliance" (Germany, Austria-Hungary, and Italy.) 
In 1905, German Chief of the General Staff, Count Alfred von Schlieffen devised an operational military plan to be used in any future two-front war against France and Russia. Known as the Schlieffen Plan, the plan's purpose was to defeat France and then Russia.

In 1914, to activate the Schlieffen Plan required the German army to cross neutral Belgium for quick access to Paris. Done on August 3, this German move ultimately brought the British into World War I because Germany's actions violated the 1839 Treaty of London Britain had guaranteed to Belgium.

Schlieffen Plan Execution in 1914

German army's path in 1914

WWI Themes

Triple Alliance (The Central Powers)

  • Germany
  • Austria-Hungary
  • Ottoman Empire
  • Bulgaria

Triple Entente (The Allied Powers)

  • Great Britain
  • France
  • Russia
  • Italy
  • Australia
  • United States
  • Serbia
  • Montenegro
  • Romania
  • Greece
  • Portugal
  • Japan
  • Brazil

Neutral Powers

  • Belgium
  • Denmark
  • Liechtenstein
  • Luxembourg
  • Netherlands
  • Norway
  • Spain
  • Sweden
  • Switzerland

Lusitania: Germans Provoke US

Why?
     When the German submarine (U-boat) U-20 torpedoed the British ocean liner Lusitania carrying 1,962 passengers on May 7, 1915, the act would ultimately trigger the United States' entry into WWI.
     Until that time, the United States had chosen to remain neutral. However, between the continued German submarine warfare and the British interception of the Zimmerman Telegram in January 1917, President Woodrow Wilson asked the United States Congress for permission to engage in war.
     Complying, Congress officially declared war on Germany and its allies on April 6, 1917.
British WWI recruitment poster reminds citizens about the torpedoed steamship 'Lusitania' by German U-boat on 7 May 1915.
The Granger Collection / Universal Images Group
RECRUITMENT POSTER, 1915. - British Recruitment Poster From World War I, Reminding Citizens Of The Sinking Of The Cunard Steamship 'Lusitania' By German Submarine On 7 May 1915.. Fine Art. Encyclopædia Britannica Image Quest. Web. 10 Nov 2011

March 22, 1918: Red Cross workers in a trench tending to a wounded American soldier on a stretcher.

Sgt Leon H. Caverly / Topical Press Agency / Getty Images / Universal Images Group Trench Aid. Photographer. Encyclopædia Britannica Image Quest. Web. 14 Nov 2011.

The Most Famous Poster

I Want You for the U.S. Army
James Montgomery Flagg (1877-1960)
I Want You for the
U.S. Army

Lithograph, 1917

Legacy of World War I