what started ww1

The immediate cause of World War I was the assassination of Archduke Franz Ferdinand of Austria-Hungary. This event took place on June 28, 1914, when a young Serbian patriot shot and killed the heir to the Austro-Hungarian Empire in the city of Sarajevo. The assassin was a supporter of the Kingdom of Serbia, and within a month, the Austrian army invaded Serbia, leading to the expansion of the war to include all those involved in the mutual defense alliances. This event triggered a series of declarations of war, ultimately leading to the outbreak of World War I.