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The trigger for the war was the assassination of Archduke Franz Ferdinand of Austria, heir to the throne of Austria-Hungary, by Yugoslav nationalist Gavrilo Princip in Sarajevo on 28 June 1914. This set off a diplomatic crisis when Austria-Hungary delivered an ultimatum to the Kingdom of Serbia, and entangled international alliances formed over the previous decades were invoked. Within weeks, the major powers were at war and the conflict soon spread around the world.
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On 28 July, the Austro-Hungarians declared war on Serbia. As Russia mobilised in support of Serbia, Germany invaded neutral Belgium and Luxembourg before moving towards France, leading the United Kingdom to declare war on Germany. After the German march on Paris was halted, with a trench line that changed little until 1917. On the Eastern Front, the Russian army was successful against the Austro-Hungarians, but the Germans stopped its invasion of East Prussia.
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The Emperor of Austria-Hungary receives the report of Austro-Hungarian investigation into the Assassination of Archduke Franz Ferdinand of Austria at Sarajevo. The Times publishes an account of the Austro-Hungarian press campaign against the Serbians (who are described as "pestilent rats").
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Austrian artillery bombards Belgrade, capital of Serbia
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The German Empire declares war on the Russian Empire, following Russia's military mobilization in support of Serbia; Germany also begins mobilization.
France orders general mobilization.
New York Stock Exchange closed due to war in Europe, where nearly all stock exchanges are already closed. -
German troops occupy Luxembourg in accordance with the Schlieffen Plan.
A secret treaty between the Ottoman Empire and Germany secures Ottoman neutrality.
At 7:00 pm (local time) Germany issues a 12-hour ultimatum to neutral Belgium to allow German passage into France. -
Germany declares war on Russia's ally, France.
At 7:00 am (local time) Belgium declines to accept Germany's ultimatum of August 2. -
German troops invade Belgium at 8:02 am (local time). Declaration of war by the United Kingdom on Germany for this violation of Belgian neutrality. This effectively means a declaration of war by the whole British Empire against the German Empire, beginning World War I from the British perspective. The United States declares neutrality.
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Germany declares war on Belgium.
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In November 1914, the Ottoman Empire joined the Central Powers, opening fronts in the Caucasus, Mesopotamia and the Sinai.