Why Did World War I Start? The Causes Explained

The spark: Sarajevo, 28 June 1914

Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, was shot in Sarajevo by Gavrilo Princip, a Bosnian Serb nationalist. Austria-Hungary blamed Serbia and decided to take a hard line.

The long-term causes

Alliances: Europe was split between the Triple Alliance (Germany, Austria-Hungary, Italy) and the Triple Entente (France, Russia, Britain).
Militarism: Great powers built large armies and navies and planned rapid mobilisation.
Imperial rivalry: Competition for colonies and trade created tension.
Nationalism: Nationalist movements, especially in the Balkans, threatened multi-ethnic empires.

The July Crisis

In late July Austria-Hungary sent Serbia an ultimatum and declared war on 28 July. Russia began mobilising to support Serbia. Germany declared war on Russia on 1 August and on France on 3 August. When Germany invaded neutral Belgium, Britain entered the war on 4 August.

Why a local crisis became a world war

The alliance system and military plans, such as Germany's Schlieffen Plan for a quick attack on France, left little room for delay. Each mobilisation pushed other states to respond, and diplomacy could not keep up.

How it ended

The war ended with the armistice of 11 November 1918. The Treaty of Versailles of 1919 formally ended the war with Germany and set harsh terms that shaped the years that followed.

Quick quiz: World Wars

On the first day of which 1916 battle did the British Army suffer about 57,000 casualties?

Answer: Battle of the Somme

On 1 July 1916, the first day of the Battle of the Somme, the British Army suffered about 57,000 casualties, its worst single day.

The Treaty of Versailles, signed in 1919, officially ended which war?

Answer: World War I

The Treaty of Versailles, signed in June 1919, formally ended World War I and imposed significant penalties on Germany.

In which year did World War II end?

Answer: 1945

World War II ended in 1945, with Germany surrendering in May and Japan surrendering in September following the atomic bombings of Hiroshima and Nagasaki.