What event sparked the onset of World War I?

The assassination of Archduke Ferdinand on June 28, 1914, is widely recognized as the immediate catalyst that ignited World War I. Ferdinand, heir to the Austro-Hungarian throne, was killed by Gavrilo Princip, a Bosnian Serb nationalist, in Sarajevo. This event set off a chain reaction of political maneuvers and alliances that ultimately led to the declaration of war.

The assassination intensified existing tensions in Europe among the major powers, particularly involving Serbia and Austria-Hungary. Austria-Hungary issued an ultimatum to Serbia, which, when not fully accepted, resulted in Austria-Hungary declaring war on Serbia. The complex system of alliances, including Germany supporting Austria-Hungary and Russia backing Serbia, quickly escalated the conflict, drawing multiple nations into war.

This pivotal moment highlights how a singular event can dramatically alter the course of history, illustrating the interconnectedness of national interests and alliances at the time.