One Piece: Absurd Justice
Thirty Nine years have passed since the fall of the Great Kingdom. In its place a new empire formed: The World Government, made up of 20 kingdoms and the 170 countries affiliated with them.
Any information regarding the Great Kingdom was banned and soon afterwards the twenty kings declared that they now be referred to as "creators" of the world. An age of piracy erupted in the anarchy of a burgeoning government. The WG established The Navy, whose marines served to enforce peace throughout its territory. The Four Emperors of the Sea, mighty pirates whose power allowed them to control nations, rose to prominence in the Grand Line and ruled over The New World.
In response, The World Government created two additional organizations. To deter its citizens from rebellion, a secretive organization known as Cipher Pol was established with the primary objectives of reporting and dealing with insubordination. To combat the pirate menace born from anarchy, the WG sanctioned pirates who could pillage and raid to their hearts' content so long as they served as a deterrence to any upcoming pirates and would obey the beck and call of the WG when needed. These were known as The Seven Warlords of the Sea.
This is a period of great change, of destruction and rebirth, but despite the importance of this time period, it wasn't well documented. Perhaps intentionally.