The July Crisis was a series of interrelated diplomatic and military escalations among the major powers of Europe in mid-1914, which led to the outbreak of World War I. It began on 28 June 1914 when the Bosnian Serb nationalist Gavrilo Princip assassinated Archduke Franz Ferdinand, heir presumptive to the Austro-Hungarian throne, and his wife Sophie, Duchess of Hohenberg. A complex web of alliances, coupled with the miscalculations of numerous political and military leaders (who either regarded war as in their best interests, or felt that a general war would not occur), resulted in an outbreak of hostilities amongst most of the major European states by early August 1914.
Following the murder, Austria-Hungary sought to inflict a military blow on Serbia, to demonstrate its own strength and to dampen Serbian support for Yugoslav nationalism, viewing it as a threat to the unity of its multi-national empire. However, Vienna, wary of the reaction of Russia (a major supporter of Serbia), sought a guarantee from its ally, Germany, that Berlin would support Austria in any conflict. Germany guaranteed its support through what came to be known as the "blank cheque", but urged Austria-Hungary to attack quickly to localise the war and avoid drawing in Russia. However, Austro-Hungarian leaders would deliberate into mid-July before deciding to give Serbia a harsh ultimatum, and would not attack without a full mobilisation of the army. In the meantime, France met with Russia, reaffirmed their alliance, and agreed they would support Serbia against Austria-Hungary in the event of a war.