The God Valley Incident is one of the most curious past events in the One Piece narrative. The event covers the defeat of the Rocks Pirates, a crew that required the combined forces of the Navy and the Roger Pirates to stop them. It's an intriguing time because it involves Monkey D. Garp and Gol D. Roger, two of the most prominent men sailing the sea at that time, teaming up to beat someone who was too great for either of them. However, the evil this crew was willing to commit compelled the World Government to erase the fight from history, which may have also included sinking the island it took place on. As such, the battle and everything surrounding it remains shrouded in mystery.
Source：https://www.cbr.com/one-piece-1095-god-valley-setup/
