Question

What system and events led to outbreak of First world war in Europe ?​

Answer 1

World War I, also known as the Great War, began in 1914 after the assassination of Archduke Franz Ferdinand of Austria. His murder catapulted into a war across Europe that lasted until 1918.

Answer 2

The immediate cause of World War I that made the aforementioned items come into play (alliances, imperialism, militarism, nationalism) was the assassination of Archduke Franz Ferdinand of Austria-Hungary. ... This assassination led to Austria-Hungary declaring war on Serbia.