The First World War was triggered by the assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, by Gavrilo Princip, a Bosnian Serb nationalist. This event set off a chain reaction due to the complex web of alliances and rivalries among European powers. Austria-Hungary declared war on Serbia, prompting Russia to mobilize in Serbia's defense. Germany, allied with Austria-Hungary, declared war on Russia and France, and invaded Belgium, pulling Britain into the conflict. Underlying tensions—nationalism, militarism, imperialism, and the alliance system—escalated the crisis into a global war.
