I didn't know where to put my crazy One Piece theory, so I will do it here. If theories and speculations are to be put somewhere else I'm sorry if this bothers anyone.
And with that, let me share my crazy One Piece theory. It came to me while I was working on some files for my aunt and watching some YouTube One Piece theories videos. As the video creator was showing Corazon's explanation to Law about the Ds being the Gods natural enemies, and the connection between the word Gods and the Tenryuubito (spelling?) I suddenly wandered why.
Why would the Tenryuubito be the Gods? According to Corazon, it was just speculation from the Celestial Dragons, believing themselves the gods. So this means that from the very beginning when the twenty kingdoms united and formed the World Government, they warned their descendants about the D.
But why did they never say that the Ds are their natural enemy? So I wandered if maybe the Gods the Tenryuubito refer to aren't themselves but the actual gods, the three Ancient Weapons named after Pluto, Poseidon and Uranus.
And BAM, inspiration struck. Since we don't know much about the history of One Piece world and the Ancient Weapons, let's start from the beginning.
A popular theory right now is that the three Ancient Weapons were created (in Poseidon's case allied) to the mysterious kingdom that disappeared circa 800 years before. But what if we are completely and totally wrong?
Considering that if such powerful kingdom had three means to destroy the world, how would it be defeated and completely erased from history? Some would say that the kingdom would never use those weapons to destroy the world and that's why they lost.
Considering the Ds we have seen so far (except Blackbeard, fudge that dude), I agree. If the Ds ARE the descendants of that great kingdom I don't see any of them actually using those weapons.
Which also makes me wander, why would they bother making/allying with them?
What if the three Ancient Weapons were under the control of the Twenty kingdoms at the beginning? What if, when the Great kingdom erased from time discovered that they set out to steal or stop those weapons from being used?
This could explain many things. For one, the Tenryuubito warning about the Ds and Gods. Since the Great kingdom concentrated their efforts on ensuring that their will would survive and keeping the weapons hidden the Twenty kingdoms were furious and feared for their weapons.
This could also explain their very active search for those Weapons. The World Government claims that Poneglyphs are dangerous because they reveal the Weapons locations but would have used Nico Robin to find them if they have the chance and use it as they see fit.
Considering this it could also explain how so many descendants survived if they are descendants of the Great Kingdom. While transporting and hiding the Poneglyphs, it makes sense they wouldn't stick around or return to their homeland, settling among villagers and hiding themselves behind the D.
How could this potentially affect the storyline? Well we know that the world will go to war when the One Piece is found (which probably has the Rio Poneglyph) in Raftel. It would be interesting if Raftel was actually the Great kingdom that fell, explaining why the Gorousei killed the O'haras before the name could be revealed.
Considering the fact that during Luffy's adventures he has found allies among two carriers of the Ancient Weapons, they could decide to set out and destroy those weapons, just like Franky destroyed the blue prints. Destroying a ship is simple, but what about Poseidon?
Considering that Joy Boy built Noah to pull Fisherman Island to the surface, using Poseidon's ability to control Sea Kings, one has to wander why he failed. The main and most likely reason he failed was because Poseidon was unable to ask the Sea Kings to pull the ship.
Why couldn't she? What is she was kidnapped by the Twenty kingdoms and forced to do their biding. Fearing for her people, the princess accepted but was later freed by someone of the Great kingdom. She would later sacrifice her voice to ensure that she could never control a Sea King again, forfeiting her position as Sea Queen.
But then what is Joy Boy apologizing for? Survivor's guilt maybe, feeling guilt from not building the ship faster or something like that. He was therefore unable to keep his promise to Poseidon of taking her to the surface, for she refused to ever go there again.
Which is a terrible echo on Luffy's promise to Shirahoshi. But let's consider this. First of all we aren't sure if Luffy is the one who destroys Fishman Island. It is possible that a man wearing a Strawhat does (World Government trying to shift the blame maybe?) and Luffy fights them.
Secondly it's possible that Luffy decides to destroy Fishman Island to ensure that the Gorusei can't use it as leverage against Shirahoshi. What if after he destroys the island the Government is forced to relocate the population, unable to manipulate Shirahoshi as they have promised the opportunity to live under the sun? Or Luffy destroys Shirahoshi's ability and somehow manages to keep his promise.
If there is one thing we have seen it's that the Government would manipulate everything as to appear blameless.