What is the Void Century?

"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?