The assassination of Archduke Franz Ferdinand on June 28, 1914, is often cited as the immediate catalyst for World War I. His death, carried out by Gavrilo Princip, a Bosnian Serb nationalist, escalated existing tensions between Austria-Hungary and Serbia. This assassination set off a chain reaction of alliances and military mobilizations, leading to the war's outbreak in August 1914. The event highlighted the fragility of European alliances and nationalist sentiments, marking a significant turning point in global history. Ultimately, World War I reshaped national boundaries, political systems, and social structures, leading to profound changes throughout the 20th century.