Funny and illuminated video:
The assassination on 28 June 1914 of Archduke Franz Ferdinand of Austria, the heir to the throne of Austria-Hungary, by a Yugoslav nationalist was the proximate trigger of the war.
On 28 July, the conflict opened with the Austro-Hungarian invasion of Serbia, followed by the German invasion of Belgium, Luxembourg and France; and a Russian attack against Germany.
- Austria-Hungary, unsatisfied with Serbia's response to her ultimatum (which in the event was almost entirely placatory: however her jibbing over a couple of minor clauses gave Austria-Hungary her sought-after cue) declared war on Serbia on 28 July 1914.
- Russia, bound by treaty to Serbia, announced mobilisation of its vast army in her defence, a slow process that would take around six weeks to complete.
- Germany, allied to Austria-Hungary by treaty, viewed the Russian mobilisation as an act of war against Austria-Hungary, and after scant warning declared war on Russia on 1 August.
- France, bound by treaty to Russia, found itself at war against Germany and, by extension, on Austria-Hungary following a German declaration on 3 August. Germany was swift in invading neutral Belgium so as to reach Paris by the shortest possible route.
- Britain, allied to France by a more loosely worded treaty which placed a "moral obligation" upon her to defend France, declared war against Germany on 4 August. Her reason for entering the conflict lay in another direction: she was obligated to defend neutral Belgium by the terms of a 75-year old treaty. With Germany's invasion of Belgium on 4 August, and the Belgian King's appeal to Britain for assistance, Britain committed herself to Belgium's defence later that day. Like France, she was by extension also at war with Austria-Hungary.
- With Britain's entry into the war, her colonies and dominions abroad variously offered military and financial assistance, and included Australia, Canada, India, New Zealand and the Union of South Africa.
- United States President Woodrow Wilson declared a U.S. policy of absolute neutrality, an official stance that would last until 1917 when Germany's policy of unrestricted submarine warfare - which seriously threatened America's commercial shipping (which was in any event almost entirely directed towards the Allies led by Britain and France) - forced the U.S. to finally enter the war on 6 April 1917.
- Japan, honouring a military agreement with Britain, declared war on Germany on 23 August 1914. Two days later Austria-Hungary responded by declaring war on Japan.
- Italy, although allied to both Germany and Austria-Hungary, was able to avoid entering the fray by citing a clause enabling it to evade its obligations to both. In short, Italy was committed to defend Germany and Austria-Hungary only in the event of a 'defensive' war; arguing that their actions were 'offensive' she declared instead a policy of neutrality. The following year, in May 1915, she finallyjoined the conflict by siding with the Allies against her two former allies.