Hello , The Great War, also known as World War I, was caused by a combination of factors including nationalism, imperialism, militarism, and the complex web of alliances between European nations. The assassination of Archduke Franz Ferdinand of Austria-Hungary in 1914 was the spark that ignited the war, but the underlying causes had been building for years. The war lasted from 1914 to 1918 and resulted in the deaths of millions of people.