Causes of World War I: Archduke Franz Ferdinand of Austria and his wife Sophie are assassinated in Sarajevo, beginning the July Crisis and providing the casus belli of World War I.

The identification of the causes of World War I remains a debated issue. World War I began in the Balkans on July 28, 1914, and hostilities ended on November 11, 1918, leaving 17 million dead and 25 million wounded. Moreover, the Russian Civil War can in many ways be considered a continuation of World War I, as can various other conflicts in the direct aftermath of 1918.

Archduke Franz Ferdinand Carl Ludwig Joseph Maria of Austria was the heir presumptive to the throne of Austria-Hungary. His assassination in Sarajevo was the most immediate cause of World War I.

Sophie, Duchess of Hohenberg was the wife of Archduke Franz Ferdinand of Austria, the heir to the Austro-Hungarian throne. Their assassination in Sarajevo sparked a series of events that led, four weeks later, to World War I.

The assassination of Archduke Franz Ferdinand was one of the key events that led to World War I. Archduke Franz Ferdinand of Austria, heir presumptive to the Austro-Hungarian throne, and his wife, Sophie, Duchess of Hohenberg, were assassinated on 28 June 1914 by Bosnian Serb student Gavrilo Princip. They were shot at close range while being driven through Sarajevo, the provincial capital of Bosnia and Herzegovina, formally annexed by Austria-Hungary in 1908.

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, resulted in an outbreak of hostilities amongst most of the major European states by early August 1914.