The war triggered by the assassination of Archduke Franz Ferdinand was World War I. Archduke Ferdinand, heir to the Austro-Hungarian throne, was assassinated on June 28, 1914, in Sarajevo by Gavrilo Princip, a Yugoslav nationalist. This event set off a chain reaction of political alliances and tensions across Europe. Austria-Hungary's declaration of war on Serbia led to Russia's mobilization to defend Serbia, followed by Germany's declaration of war on Russia. The ensuing conflict expanded to include multiple nations, resulting in a devastating global war that lasted from 1914 to 1918, fundamentally altering the geopolitical landscape.