Causes of the First World War (Years 9–11) — History

How alliances, empire, militarism and nationalism turned one assassination in 1914 into a world war.

By 1914 the great powers of Europe had built rival alliances, huge armies and empires. When a single shot was fired in Sarajevo, the whole system tipped into war within weeks.

Why this matters Understanding how a local crisis became a global catastrophe teaches us how fear, pride and rigid plans can pull nations towards a conflict none of them fully intended.

The long-term causes: MAIN

Historians often use the word MAIN to remember four deep causes: Militarism (Britain and Germany raced to build the most powerful warships, the dreadnoughts), Alliances (Europe split into two armed camps), Imperialism (rivalry over colonies and trade), and Nationalism (intense pride, and Serb desire for freedom, made the Balkans a "powder keg").

A promise to defend one ally could pull every member of a bloc into war — the mechanism that turned a regional crisis into a world war.

The spark: Sarajevo, June 1914

On 28 June 1914 Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, was assassinated in Sarajevo by Gavrilo Princip, a Bosnian Serb nationalist. Austria-Hungary blamed Serbia and issued harsh demands.

Common exam mistake: writing that the assassination alone 'caused' the war. It was the spark, not the fuel — the MAIN causes had been building for decades, and the assassination simply triggered the alliance chain reaction.

The slide to war

Germany's Schlieffen Plan required a fast strike through neutral Belgium to defeat France before turning to face Russia, and rigid mobilisation timetables meant that once armies began to move, leaders felt unable to stop.

Put the slide to war in order:

Austria-Hungary declares war on Serbia
Russia mobilises to defend Serbia
Germany declares war on Russia and France
Germany invades neutral Belgium
Britain enters the war (4 August 1914)

Exam technique: for an 'explain why' question, work through MAIN as a checklist and link each cause to the next — examiners reward answers that show how the causes connected, not just a list.

One murder did not "cause" the war on its own — it lit a fuse on causes that had been building for decades.