What if Rocks won at God Valley, defeating both Garp & Roger and somehow subdued the Gorosei & Celestial Dragons to make himself the king of the world, Im.
Rocks becoming the king of the world would have spelt the end for the Rocks Pirates crew. He wiped out God Valley from the maps of the world and to keep his old name Rocks D. Xebec a secret to maintain the status quo.
It could be that the reason Garp is so touchy about the God Valley incident isn’t because he was forced to work with Roger but because it was a defeat and an active lie the World Government is telling even the Marines. Garp mentioned that the Rocks Pirates coming back would be a problem but that could simply mean that figures like Big Mom & Kaido who were formerly members of Rocks Pirates know about Im and seeing as the crew was never stable because it was made up of crew mates that would rival each other and had the qualities of captains they want Im’s throne, we know Kaido wants to bring the great war and we know he also wants the One Piece, we also know that the great war will come about after Luffy finds the One Piece so maybe they are directly linked.
Roger actively started trying to find the One Piece after the God Valley incident, he could have come across a Poneglyph or some information at God Valley (or that led him to God Valley) that eventually sent him on his quest to find Laugh Tale. Roger later realized he was too early to bring the dawn of the world, he died sending people to search for the One Piece and even sired a son in hopes that the son would be the one to bring the dawn, to defeat the man who defeated him, Rocks D. Xebec.
The “D. Clan” could be born in piars to do this dance, a Joy Boy and a King of the world both with the initial D.
Luffy & Blackbeard, Roger & Rocks, the original Joy Boy who owned the giant strawhat and the first King of the World Government 800 years ago. The reason Im (Rocks) might have had the picture of Luffy in a straw hat while looking at the giant straw hat is because the straw hat which represents the simple life, freedom is the enemy of he who wears the crown, king of the world and a straw hat will topple the crown like a peasant farmer uprising to topple the royal government.
I theorize that if Im really is Rocks and is the current king of the world then he’d be very old by now(older than Whitebeard, probably Roger’s age), perhaps Blackbeard will try to take his place like Rocks had done with the “D.” King of the world before him and there’ll be a new war, a new God Valley Incident in which Luffy faces Blackbeard but with bigger stakes and more players, Luffy wins, topples the World Government and brings the dawn of the world. Roger was waiting for a man, a “D.”, but Blackbeard is not that man, it’s Luffy.
*Theory by Yohananironsidev2
