World War I started in 1914. The conflict began on July 28, when Austria-Hungary declared war on Serbia, following the assassination of Archduke Franz Ferdinand. The war quickly escalated, drawing in multiple nations through a complex web of alliances. Major global powers divided into two main factions: the Allies and the Central Powers. Lasting until November 11, 1918, the war resulted in significant geopolitical changes and massive casualties. It set the stage for future conflicts, including World War II, and greatly influenced international relations and military strategies in the 20th century.