According to Greek legend, the first woman, Pandora, was actually sent as a curse to Zues' men (See, you knew it was true, guys) and was given a present upon her marriage. The present was a box that she was told never to open. Needless to say her curiosity got the better of her (like eating forbidden fruit) and she unleashed eight demons unto the world. The first seven being the seven deadly sins, and the last, which she managed to capture, was hope.
Today, much like christianity's idea of biting forbidden fruit, opening pandora's box refers to getting into a situation over which one has very little control over.
The assassinating on Austrian Archduke ferdinand in 1914 opened pandora's box for Europe.