28 June: Archduke Franz Ferdinand, heir to the Austrian throne, and his wife, visit Sarajevo in Bosnia, a province of the Austro-Hungarian Empire. A lone assassin, Gavrilo Princip, shoots and kills them both. Austria believes the killer is linked to the Serbian nationalist movement.
23 July: Austria-Hungary, with the backing of Germany, delivers an ultimatum to Serbia. The Serbs offer to submit to arbitration, but also begin to mobilize their army.
25 July: Austria-Hungary cuts diplomatic ties with Serbia and begins to mobilize.
26 July: Britain tries to convene a conference of the major European powers to resolve the situation. France, Italy and Russia agree to take part. Germany refuses.
28 July: Austria-Hungary declares war on Serbia.
29 July: Britain calls for international mediation. Russia urges German restraint, but then begins partial troop mobilization as a precaution. The Germans warn Russia, and then begin to mobilize.
30 July: Austria shells Belgrade, the Serbian capital.
31 July: Russia begins full mobilization.
1 August: Germany declares war on Russia. France and Belgium begin full mobilization.
3 August: Germany declares war on France and invades neutral Belgium. Britain delivers an ultimatum to Berlin demanding withdrawal from Belgium. Germany ignores it.
4 August: Britain declares war on Germany. The declaration is binding on the British Empire, including Canada, Australia, New Zealand, India and South Africa.
6 August: Austria-Hungary declares war on Russia.
19 August: President Woodrow Wilson announces that United States will remain neutral.
23 August: Battle of Mons.
26 August: Battle of Tannenberg (East Prussia) begins.
5 September: Battle of the Marne begins.
19 October: Battle of Ypres (‘First Ypres’) begins.
29 October: Turkish fleet bombards Russian Black Sea coast.
1 November: Russia declares war on the Ottoman Empire.
5 November: France and Britain declare war on the Ottoman Empire.