"The Void Century is a period of 100 years that has remained largely undocumented. The events of this time-period are dubbed to be the “true history” of the world, whose study has been forbidden by the World Government."
https://www.epicdope.com/what-is-the-void-century-what-happened-during-that-time/
Everything We Know About The VOID CENTURY | One Piece | Grand Line Review
The Void Century Mystery?