User blog comment:Gemini12/How long has the world had the 3 great powers/@comment-4493594-20120624085704

The WG was established after the Void Century, so about 800 years ago. The Shichibukai exist for at least 52 years, seeing how Brook knew about them even after spending decades in the devil sea.

(behold my speculations:)

My guess is that the Shichibukai have developed from alliances of the WG with pirate crews, formed in order to stop the pirates from raiding certain areas in times when the Marines were short on hands. Possibly shortly after the forming of the WG as war and times after it are a paradise for bandits and pirates. This assumption is based on how they keep replacing Shichibukai.

As for the Yonko, it is likely that as such they were established during Roger's time or a few years after his execution, with pirates of the old times becoming Yonko due to the flood of wanna-bes who became pirates to search for One Piece. This assumption is based on the lack of known former Yonko.

There is also the possibility that the Yonko existed before and the Shichibukai were formed to counter them. In that case I would assume that Roger himself was one. But that is only a theory based on how I cannot imagine Shanks taking down a former Yonko. He just doesn't seem the type to do so. It is likelier that he simply kept protecting his captain's territory. (<If that is the case I can imagine why Teach approached Shanks. Taking the territory after the captain died is what Teach did.)

Whatever the case, yes, the 3 great powers probably existed while Roger was alive.