Why did the assasination of the arch duke in Austria-hungary play such a pivotal part in the starting of world war 1?

by [deleted]

What I'm attempting to ask is, Austria-Hungary didn't really do anything before the war (at least as far as I can tell) , so why did they play such a pivotal part in the starting on world war 1?

Notamacropus

What do you mean when you say "didn't really do anything before the war"?