On July 28, 1914, the Austro-Hungarian Empire declared war on Serbia, marking the official start of World War I. This conflict arose from a complex web of alliances and tensions in Europe, particularly following the assassination of Archduke Franz Ferdinand of Austria on June 28, 1914. The declaration of war set off a chain reaction, as countries began to mobilize their forces. Germany supported Austria-Hungary, while Russia mobilized to defend Serbia. This escalation led to a global conflict that would last until 1918, involving many nations and resulting in significant loss of life and changes to the political landscape.