How did the assassination of Archduke Franz Ferdinand in Sarajevo lead to World War I?

The assassination of Archduke Franz Ferdinand in Sarajevo on June 28, 1914, served as the immediate catalyst for World War I. The act was carried out by Gavrilo Princip, a member of a Bosnian Serb nationalist movement supported by the Black Hand, which sought to liberate South Slavs from Austro-Hungarian rule.123

Austro-Hungarian officials viewed the assassination as a long-awaited opportunity to eliminate the threat posed by Serbia to the empire's integrity. With the assurance of support from Germany, Austria-Hungary issued an intentionally unacceptable ultimatum to Serbia on July 23, 1914. Although Serbia accepted most demands, it rejected terms that would have compromised its sovereignty.43

Austria-Hungary declared war on Serbia on July 28, 1914. This localized conflict rapidly escalated into a global war as the alliance systems—the Triple Alliance and the Triple Entente—triggered a chain reaction of mobilizations and declarations of war among the Great Powers, including Russia, France, and Great Britain.53