Which major world conflict broke out in 1914?

Nothing new on the West front is great book and movie (actually there are 3-4 films with that name) which are about this awful and devastating war. Must watch (read)!

Player #53553731, Who puts a thumbs down when someone says war is horrible, no to war!!!

Only the power hungry lunatic leaders crave for wars. Full well knowing that there will be blood baths committed and they will always end up with sadness.

Started due to the assassination of an heir to a throne. Or a multitude of other reasons?