my view is that the ancient kingdom was ruled by joyboy and imu together. due to rapid technological advancement, they started to argue. joyboy, carless as luffy, wanted to go ahead, with no breaks. imu wanted to supress technology, just like people today want to regulate ai, gene editing and so on. imu persuaded the kings of islands in the sphere of influence of the ancient kingdom. they sided with him against joyboy, who lost the battle. imu got his wish, the world went back technologically, as we found out during egghead.