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History guide

The causes of World War I

Militarism, alliances, imperialism, and nationalism explained, plus the assassination in Sarajevo and the July 1914 chain of events that turned a crisis into a world war.

World War I began in the summer of 1914 and lasted until November 1918. Historians usually separate the long-term causes that made Europe dangerous from the short-term trigger that set the war off. A common memory aid for the long-term causes is MAIN.

M: Militarism

The great powers built large armies and drew up detailed war plans. Britain and Germany raced to build battleships after Britain launched HMS Dreadnought in 1906. Germany's Schlieffen Plan assumed a quick strike through Belgium against France before turning east to face Russia.

A: Alliances

Europe was split into two blocs: the Triple Alliance (Germany, Austria-Hungary, and Italy) and the Triple Entente (France, Russia, and Britain). Alliances were meant to deter war, but they also meant a local conflict could pull in every major power.

I: Imperialism

Competition for colonies and influence, especially in Africa and the Balkans, created rivalries and repeated diplomatic crises in the years before 1914.

N: Nationalism

Intense national pride fed rivalry between the powers, while Slavic nationalism in the Balkans threatened multi-ethnic Austria-Hungary. Serbia, backed by Russia, wanted to unite South Slavs, including those living under Austro-Hungarian rule.

The trigger: Sarajevo, June 28, 1914

Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, was assassinated in Sarajevo by Gavrilo Princip, a Bosnian Serb linked to the Black Hand, a Serbian nationalist secret society.

The July Crisis

  1. Germany promised Austria-Hungary full support, often called the "blank check."
  2. July 23: Austria-Hungary sent Serbia a harsh ultimatum. July 28: it declared war on Serbia.
  3. Russia began mobilizing to support Serbia.
  4. August 1 and 3: Germany declared war on Russia, then on France.
  5. August 4: German troops invaded Belgium, and Britain declared war on Germany, citing the violation of Belgian neutrality.

Italy did not join its allies in 1914. It entered the war on the Allied side in 1915.

Writing about the causes

Strong essays do not just list MAIN. They rank the causes and argue which mattered most, for example by showing how the alliance system turned a regional Balkan crisis into a continental war within a week.

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