On this date in 1914 Archduke Franz Ferdinand of Austria and his wife Sophie were assassinated in Sarajevo by Serbian nationalist Gavrilo Princip. The murders sparked World War I.
Dan Carlin has an excellent in depth (and I mean in depth) podcast on the events surrounding the assassination in his Blueprint for Armageddon. Well worth the listen.
If your tastes run more towards video rather than audio check out the Great War on YouTube.
Both are great sources of history.