Went down a rabbit hole since this drop about two destructions.
It seems that, based on Enel’s cover story, the moon people ran out of resources and came to earth. These were the Lunarians. They brought with them, guess what, advanced robotic technology. These robots are currently activated and serving Enel on the moon.
They came to a world of chaos, not ruled over by one particular group, but divided between gods and demons and the humans under their control. There were also many races of human, such as the long leg and long arm tribes, alongside creatures like Fishmen and Giants. The balance of power was disrupted by the arrival of these lunar beings and their advanced technology, who potentially were displaced from the moon by some action from Imu or the other devils. They joined forces with Nika, or Joyboy, to destroy the devils.
The ancient weapons were used during this time, with the wielders of the weapons being unwilling to share them with anyone else, leading to the conflict. Joyboy espoused nuclear proliferation for mutual assurance. Imu and allies wanted the weapons so they could be in control. One Piece is social commentary on world history following World War 1, with the comments on Elbaf, as well as the running commentary on the Celestial Dragons’ depravity and corruption, as the end result of woke ideology mingled with disgusting greed and climate destruction in this world where nuclear missiles are kept by the powerful.
Joyboy lost the conflict, the allied nations became the WG (literally the United Nations), their rulers at the time became the Tenryuubito, and the history was destroyed so that people would not find out that the ones ruling them are actual devil monstrosities. This represents the period of Japanese history essentially lost to the world during the time of World War 2, when the well-organized Japanese allied themselves with literal devils in pursuit of a greater objective, but they were relegated to villains by history as the allies of Hitler.
They made their base on the Red Line, creating it some way or another, by using Uranus to raise the world’s sea levels and sink their enemies. They chose to do it right by the Sun Tree Eve because that is where devil fruits come from. The devil fruits are the displaced souls of the devils who died in the conflict captured by the sun tree. They are immortal spirits who are not destroyed but kept through the fruits and recycled when they die, as potentially all spirits are in this world. There is some plan in the works to revive them all and take over the world again. Those with the D initial are those who have the ability to destroy devil’s souls by consuming the fruit.
Blackbeard is both a D and a Buccaneer descendant, giving him the ability to not only destroy the spirits of the devils he consumes but also to consume multiple. Either that or the darkness fruit gives him the ability to house as many devil spirits as he wants since his soul is now a dark abyss.