So I randomly thought of this theory in the car today, and felt like sharing it.
Main Point: Garp and/or Sengoku founded SWORD
Reasoning:
I think that Garp and/or Sengoku founded SWORD at one of two times. Either
After God Valley
During Roger’s imprisonment
Whichever one it is, I think that either Rocks or Roger mentioned something about the true history(yes I think Rocks probably knew something about it), specifically the existence of Im. This revelation then led Garp to tell Sengoku, who came up with the idea of SWORD, a secret marine organization dedicated to spying on the Yonko in order to assemble the poneglyphs before they can, find the true history, and reveal it to overthrow Im.
In addition to this, I think Aokiji is a member, likely the current leader of the organization. This is due to him “leaving” the marines during the timeskip, and allying with the Blackbeard Pirates. I believe that the whole battle was planned, in order to make the world believe that Aokiji truly left the marines, in order to lessen suspicion that he may be a spy. Of course, this would imply that either Akainu was in on it, or that Aokiji simply tricked him. Personally, I doubt Akainu is part of the group, given his seemingly blind loyalty to the World Government(although that would be a perfect cover for it, now that I think of it). I believe this was implied when Aokiji saved Smoker on Punk Hazard, telling him “I’m still me,” possibly referring to still secretly being a marine.