What event was triggered by the assassination of Archduke Franz Ferdinand?

The assassination of Archduke Franz Ferdinand in June 1914 served as the catalyst for the outbreak of World War I. His death set off a chain of events involving entangled alliances and escalating tensions among European powers, ultimately leading to a declaration of war. The archduke was the heir to the Austro-Hungarian throne, and his assassination by a nationalist who sought independence for Slavic peoples prompted Austria-Hungary to issue an ultimatum to Serbia.

This ultimatum triggered Russia, an ally of Serbia, to mobilize in defense of its Slavic kin, which in turn led Germany to declare war on Russia. The complex web of alliances meant that what began as a regional conflict escalated into a full-scale world war, involving nations across Europe and beyond. The other options listed do not relate directly to the events immediately following the assassination, making this choice the only accurate representation of the resulting historical moment.