This is just a theory that I’ve been thinking about for quite some time. I believe the Rocks Pirates got created from having a big Davy Back Fight.
In Chapter 306, Robin explains to us that the Davy Back Fight is a Pirate Game that originated a long time ago on Pirate Island, a Pirate Paradise. It was a game to steal Pirates from other crews to get the best Pirates on your crew.
Then in Chapter 925, Blackbeard calls his home island the Pirate island and claims that it’s a Pirate Paradise.
Finally, in Chapter 957, Sengoku explains that the Rocks Pirates Crew were created and came together on the Pirate Island, the island that Blackbeard is currently occupying.
After seeing people like Whitebeard, Big Mom, Kaido and even Shiki, it’s impossible to believe that any of them would ever be able to be in the same crew. Three of them had Conqueror’s Haki and I bet Rocks D. Xebec probably had it too. Even Whitebeard didn’t want Oden to join his crew at first because he knew what type of person he was, someone who doesn’t like serving under people.
So here’s my theory. I believe Rocks D. Xebec had a Davy Back Fight to get all these people in his crew. We all know how confident Big Mom, Kaido, Whitebeard are in their strength and wouldn’t turn back from a challenge. Luffy didn’t turn back either from the challenge. And the future emperors lost and probably had to work under Rocks until they got defeated.
*Theory by Mugiwara300