The July Crisis was a diplomatic crisis among the major powers of Europe in the summer of 1914 that led to the First World War. Immediately after Gavrilo Princip, a Bosnian Serb nationalist, assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, in Sarajevo, a series of diplomatic maneuverings led to an ultimatum from Austria-Hungary to Serbia, and ultimately to war.

This ultimatum was part of a coercive program meant to weaken the Kingdom of Serbia as a threat to Austria-Hungary's occupation of the northern Balkans which had a significant southern Slavic population, including a majority Serbian community in Bosnia. This was supposed to be achieved either through diplomacy or by a localized war if the ultimatum were rejected. Austria-Hungary preferred war, though Istvan Tisza hoped that the ultimatum would be reasonable enough that it would not be rejected outright.

One month after the assassination of Franz Ferdinand, Austria-Hungary declared war on Serbia, thus initiating the First World War.