One Piece: How Powerful Was The Great Kingdom?

The first mention of the Great Kingdom, which was the enemy of the World Government during the Void Century in One Piece, came during a flashback to the Ohara Incident. When cornered by CP9 for his research into the Poneglyphs and the ancient script used to write them, Professor Clover — the director of the Ohara Library and a world renowned archaeologist who mentored Nico Robin — spoke to the Five Elders through a Den Den Mushi. During this conversation, when the scholars of Ohara learned that they had been condemned to death, Clover mentioned that he knew of certain secrets from the Void Century. He then proceeded to berate the Five Elders, for hiding the true history of the world by citing the threat of the Ancient Weapons being revived.