What caused World War I?

Long-term and short-term causes

Historians separate the causes of a war into long-term conditions that made conflict likely and short-term events that set it off. A useful image is a room full of dry fuel and a spark. In 1914, decades of rivalry, arms building and rival alliances were the fuel; a political murder in the Balkans was the spark.

The acronym MAIN is a classroom summary of the long-term causes. It helps you remember them, but it is a simplification. To explain the war well, you also need to know what happened in the summer of 1914 and the choices leaders made then.

M is for militarism

Militarism means a belief in building strong armed forces and preparing to use them. In the decades before 1914, the great powers expanded their armies and introduced conscription, so millions of trained reservists could be called up quickly.

Britain and Germany ran a naval arms race. Britain launched HMS Dreadnought in 1906, a battleship so advanced that it made earlier ships outdated, and Germany raced to build its own. Generals also drew up detailed war plans. Germany's Schlieffen Plan assumed a war with both France and Russia and called for defeating France quickly by marching through neutral Belgium before turning east. Plans like this meant that once one country mobilized, others felt they had to move fast too.

A is for alliances

By 1914, Europe was divided into two groups of powers:

These were mostly defensive agreements, and they did not automatically force anyone to fight. But they meant that a local conflict involving one member could draw in its partners. When the war came, Italy stayed neutral in 1914, arguing that the Triple Alliance was defensive, and in 1915 joined the war against Austria-Hungary.

• The Triple Alliance: Germany and Austria-Hungary (allied since 1879), joined by Italy in 1882.
• The Triple Entente: France and Russia (allied by 1894), Britain and France (the Entente Cordiale of 1904), and Britain and Russia (the Anglo-Russian Convention of 1907). The ententes were friendly understandings, not binding promises to go to war.
• Treaty guarantees: Britain, France, Prussia and others had signed the Treaty of London in 1839, guaranteeing Belgium's neutrality.
• Russia saw itself as the protector of Serbia and other Slavic peoples, though it had no formal alliance with Serbia.

I is for imperialism, N is for nationalism

Imperialism is the building of empires by taking control of other lands. By 1914, European powers had divided most of Africa and much of Asia among themselves. Germany, unified only in 1871, wanted a larger empire and "a place in the sun." Rivalry over colonies produced crises, such as the two Moroccan crises of 1905 and 1911, in which Germany challenged French influence in Morocco and Britain backed France, drawing the two closer together.

Nationalism is strong loyalty to one's nation and, often, the belief that each nation should rule itself. It worked in two directions. It made great powers proud and quick to feel insulted; France, for example, resented losing Alsace-Lorraine to Germany in 1871. It also drove peoples inside empires to seek independence. In the Balkans, Austria-Hungary had annexed Bosnia and Herzegovina in 1908, angering Serbian nationalists who wanted the region's South Slavs united with Serbia. Two Balkan Wars in 1912 and 1913 enlarged Serbia and raised tension with Austria-Hungary further.

The assassination in Sarajevo, June 28, 1914

Archduke Franz Ferdinand, heir to the throne of Austria-Hungary, visited Sarajevo, the capital of Bosnia, with his wife Sophie on June 28, 1914. A group of young Bosnian Serb conspirators had come to kill him, armed with weapons supplied with help from the Black Hand, a secret Serbian nationalist society with links to Serbian military officers.

That morning one conspirator threw a bomb at the Archduke's car; it bounced off and wounded people in the car behind. Later, the Archduke's car took a wrong turn and stopped near where Gavrilo Princip, a 19-year-old member of the group, was standing. Princip shot and killed both Franz Ferdinand and Sophie.

Austria-Hungary's leaders blamed the Serbian government and saw a chance to crush Serbian nationalism. Before acting, they asked Germany for support. On July 5 and 6, Germany promised to back Austria-Hungary whatever happened, a pledge historians call the "blank cheque."

The July Crisis: the alliance chain, day by day

In about five weeks, a crisis between two countries became a European war:

• July 23, 1914: Austria-Hungary sends Serbia an ultimatum with harsh demands and a 48-hour deadline.
• July 25: Serbia accepts most of the demands but not all; Austria-Hungary breaks off relations. Serbia had already begun to mobilize its army.
• July 28: Austria-Hungary declares war on Serbia.
• July 30: Russia orders general mobilization in support of Serbia.
• August 1: Germany declares war on Russia.
• August 3: Germany declares war on France, following the Schlieffen Plan.
• August 4: German troops enter neutral Belgium. Britain, citing Belgian neutrality and its ties to France, declares war on Germany.
• August 6 and after: Austria-Hungary declares war on Russia, and within days France and Britain declare war on Austria-Hungary. Japan joins the Allies on August 23, and the Ottoman Empire enters the war on Germany's side that autumn.

Who was to blame? How historians disagree

The Treaty of Versailles, signed on June 28, 1919, five years to the day after the assassination, included Article 231, often called the war guilt clause. It made Germany and its allies accept responsibility for the loss and damage of the war, mainly as a basis for reparations.

Historians have argued ever since. In the 1960s the German historian Fritz Fischer argued that Germany's leaders deliberately pursued a war to expand their power. Others have spread responsibility more widely: Austria-Hungary chose war on Serbia, Russia mobilized early, France encouraged Russia, Britain did not make its intentions clear, and Serbian nationalists set the crisis in motion. Christopher Clark's book The Sleepwalkers (2012) argued that leaders in several capitals stumbled into a war few fully wanted. A strong answer weighs these views with evidence rather than blaming a single country.

Common mistakes and how to study

Avoid these errors in essays and on tests:

To study, build a timeline from 1871 to August 1914, colour-coding events by MAIN category, and add the July Crisis dates above. Then practise ranking the causes: write a paragraph arguing which was most important and why, using at least two dated events as evidence. Checking every date against a reliable reference before you hand in work is a good habit.

• Saying the assassination alone caused the war. It was the trigger; the long-term causes explain why it led to a world war rather than a local one.
• Saying the alliances forced every country to fight automatically. Italy did not; Britain's decision also turned on Belgian neutrality.
• Mixing up the sides. Germany and Austria-Hungary (later with the Ottoman Empire and Bulgaria) formed the Central Powers; France, Russia and Britain led the Allies.
• Getting the US date wrong. The United States entered the war in April 1917, not 1914. The fighting ended with the armistice of November 11, 1918.