I came up with an interesting theory about the void century, which was basically a war between the ancient kingdom which wanted peace with the non human groups and the world government who wanted to enslave the non human groups. I think the world government has only 20 kings and there is no way that only 20 kings could have won just because of manpower and strength.
I think the 20 kings who formed the world government won the war because they stole the ancient weapon Pluton which was intended to destroy the red line and join all the seas to form one piece. There is no way the king of ancient kingdom which was Joyboy could have been defeated easily. I mean he possessed the ancient weapon Poseidon and I aim not sure about who had the Uranus. And he also possessed the voice of all creation and the military strength of the all non human groups. So it makes it clear that the world government used the ancient weapon Pluton and yes it was destroyed by someone from the ancient kingdom.
I guess when the world government used Pluton on ancient kingdom and the ancient kingdom was destroyed, after losing all of his nakama and friends, the ancient kingdom was left with nothing but a few of their forces. Then I guess the King of the Ancient Kingdom used all of his power to destroy the ancient weapon Pluton and afterwards says that weapons are weapons, it doesn’t matter how the creator of the weapon intends to use it, it is the owner who decides how to use it… And then I guess he escapes with heavy wounds and finally until his death he encrypts the poneglyphs and desires that the history and the ideals should not be lost in the course of time… then maybe the great war ends and the world government was formed.
About the celestial dragons, they were the royal family of the twenty countries that were fighting the ancient kingdom. I think back in the history, they were not dumb as they are now excluding the Gora-sai. They are all almost the same, they need slaves and they bullshit everything in their path… And I think they were too intelligent back in time… And there is also a theory in my mind that the war didn’t last more than a half a year, after winning the war within half or more years, they were doing the cover ups to hide the true history of the ancient kingdom.
As clover from Robin’s past revealed that the world government don’t fear the ancient kingdom, they feared the ideals of the ancient kingdom… And I guess that leaves us with a conclusion that in the 100 year void century the 20 kings were gathering up arms and gaining power, they established the Marines with ideal of fraternity and protection from bad people and they were building up reputation as the good guys. They banished the reading of poneglyphs and anyone involved with it must die. I think around the reverie arc it will be revealed the foreshadowing of the true history .