World War I
July Crisis

The assassination initiated the July Crisis, a month of diplomatic manoeuvring between Austria-Hungary, Germany, Russia, France and Britain. Believing that Serbian intelligence helped organise Franz Ferdinand's murder, Austrian officials wanted to use the opportunity to end their interference in Bosnia and saw war as the best way of achieving this. However, the Foreign Ministry had no solid proof of Serbian involvement. On 23 July, Austria delivered an ultimatum to Serbia, listing ten demands made intentionally unacceptable to provide an excuse for starting hostilities.

Serbia ordered general mobilization on 25 July, but accepted all the terms, except for those empowering Austrian representatives to suppress "subversive elements" inside Serbia, and take part in the investigation and trial of Serbians linked to the assassination. Claiming this amounted to rejection, Austria broke off diplomatic relations and ordered partial mobilisation the next day; on 28 July, they declared war on Serbia and began shelling Belgrade. Russia ordered general mobilization in support of Serbia on 30 July.

Anxious to ensure backing from the SPD political opposition by presenting Russia as the aggressor, German Chancellor Bethmann Hollweg delayed the commencement of war preparations until 31 July. That afternoon, the Russian government were handed a note requiring them to "cease all war measures against Germany and Austria-Hungary" within 12 hours. A further German demand for neutrality was refused by the French who ordered general mobilization but delayed declaring war. The German General Staff had long assumed they faced a war on two fronts; the Schlieffen Plan envisaged using 80% of the army to defeat France, then switching to Russia. Since this required them to move quickly, mobilization orders were issued that afternoon. Once the German ultimatum to Russia expired on the morning of 1 August, the two countries were at war.

At a meeting on 29 July, the British cabinet had narrowly decided its obligations to Belgium under the 1839 Treaty of London did not require it to oppose a German invasion with military force; however, Prime Minister Asquith and his senior Cabinet ministers were already committed to supporting France, the Royal Navy had been mobilised, and public opinion was strongly in favour of intervention. On 31 July, Britain sent notes to Germany and France, asking them to respect Belgian neutrality; France pledged to do so, but Germany did not reply. Aware of German plans to attack through Belgium, French Commander-in-Chief Joseph Joffre asked his government for permission to cross the border and pre-empt such a move. To avoid violating Belgian neutrality, he was told any advance could come only after a German invasion. Instead, the French cabinet ordered its Army to withdraw 10 km behind the German frontier, to avoid provoking war. On 2 August, Germany occupied Luxembourg and exchanged fire with French units when German patrols entered French territory; on 3 August, they declared war on France and demanded free passage across Belgium, which was refused. Early on the morning of 4 August, the Germans invaded, and Albert I of Belgium called for assistance under the Treaty of London. Britain sent Germany an ultimatum demanding they withdraw from Belgium; when this expired at midnight, without a response, the two empires were at war.
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