Austria-Hungary declares war on Serbia

On July 28, 1914, Austria-Hungary declared war on Serbia, one month after the assassination of Archduke Franz Ferdinand in Sarajevo. Austria-Hungary had issued a deliberately stringent ultimatum on July 23, demanding suppression of anti-Austrian organizations and participation in the internal investigation. Serbia accepted most terms but rejected foreign involvement in its judicial process. The declaration triggered a cascade of alliance obligations — Russia mobilized in defense of Serbia, prompting Germany to declare war on Russia, then France, drawing in Britain. Within weeks, the conflict expanded into a general European war.