Historians writing about the origins of World War I have differed over the relative emphasis they place upon the factors involved. Changes in historical arguments over time are in part related to the delayed availability of classified historical archives. The deepest distinction among historians remains between those who focus on the actions of Germany and Austria-Hungary as key and those who focus on a wider group of actors. Meanwhile some historians, such as Fritz Fischer, maintain that Germany deliberately sought war while others do not. The main distinction among the latter is between those who believe that a war between the "Great Powers" was ultimately unplanned but still caused principally by Germany and Austria-Hungary taking risks, and those who believe that either all or some of the other powers, namely Russia, France, Serbia and Great Britain, played a more significant role in risking war than had been traditionally suggested.

The July Crisis was a series of interrelated diplomatic and military escalations among the major powers of Europe in the summer of 1914, which led to the outbreak of World War I. The crisis began on 28 June 1914, when Gavrilo Princip, a Bosnian Serb nationalist, 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.