Octopi might be able to form a society. They’re as clever as humans, sometimes even smarter, if you believe all the stories.

But they die right after their eggs hatch, so they don’t have the sort of continuity that human societies have. They only live about a year. The only way to establish continuity is for one of them to avoid having eggs long enough to figure out how to create a system of information transfer that can be stored, like writing or Quipu. Then, of course, they would have to figure out how it can be stored safely in such a corrosive environment as the sea.

But once that’s taken care of, the record repositories would become sacred, because they would be the way young Octopi learned the majority of the information generated by Octopus society. There would not be many adults around to tell them how to grow up and become part of The Squishy Confederacy. Young octopi who refused to learn from the sacred texts would be either executed, or directed to mate and die to produce a more compliant generation.

Eventually, a mighty ocean-based society would emerge. Fairly primitive, in terms of technology, because let’s face it, electricity underwater is a hard thing to manage. But they would have metal. There’s plenty of ships littering the ocean floor. If one of these ships was sunk with its functions largely intact, the Octopi could study the mechanical processes, scavenge the parts, and develop non-electric machines. Perhaps of the clockwork variety, or cranked in some fashion.

And humans who dived into coral reefs would discover that they were being dug up by some unknown mining operation. No government or criminal organization would claim responsibility.

Nor would it be easy to tell who was actually operating these machines. Octopi can camouflage themselves easily, after all. They would only come out of hiding when the humans attempted to stop their operations.

Then the Great Ocean War would begin, as submersibles and submarines battled to save the Coral reefs from the very creatures that inhabited them. Too late! Too late! The Octopi have discovered how to find cracks in the mysterious metal shapes that descend upon them. Worse, the mined coral jams very well into the various ports and openings of a submersible. Whoever these creatures are attacking them from the world above theirs, they prove extremely vulnerable once their craft is broken open -- they don’t seem to be able to survive without it, and the few that can have these metal structures on their backs that supply them with...some form of bubbles. The Octopi don't know, except that these humans tend to die when the cord between their metal things and their mouths is severed. The bubbles fly out of the hollow cord quickly, and the human either rushes to the surface, or a bunch of bubbles come out of their mouth and they stop moving.

How fragile these creatures are!

Then one day, the Squishy Confederacy spots a very large shape passing overhead, making the awful rumbling racket they have come to associate with attacking humans. It's time to defend! Tens of thousands of tiny warriors covered in shells and armed with eight spears of coral each swarm the great metal mass, aiming for any joint, any port, any crack they can find. Slowly the gaps widen and water pours into the structure, and Octopi squirm their way inside. For the first time, the Octopi can see humans operating in their natural habitat. They seem to breathe air, like the great sea-mammals that go after Giant Squids. They have some form of internal structure that allows them to stand upright in the midst of the gravity that you now find so crushing. They also have their own spears, and knives, and curious box things that go bang. A few of your fellows die, but the rest swarm throughout the ship.

By now, as the ship begins to fill with water. your brethren have subdued all the humans they can find, and are examining the internal structures of the ship. One of you has their tentacles splayed over a flat surface that has many raised, glowing bumps. Another is turning something stuck on a wall that turns. Suddenly the ship rumbles, and there is a mighty roaring from within.

As the ship settles slowly onto the seabed, you recieve reports from your brethren who were outside the ship. from what they could see, two massive cylinders arose from within the ship and flew high into the sky.

The creatures from above stop attacking after that. Huh. Wonder where they went?