Sometime around the end of World War II, the Oracle of Delphi delivered a prophecy stating that the next child of the Big Three to turn sixteen could be responsible for saving or destroying Olympus. The Big Three had also been watching the war below, as it was fought between their demigod children and they agreed that they were influencing mortal events too much. Because of the potential danger of the Great Prophecy, and the fact that World War II was fought between their children, they vowed to have no more children with mortals.