Overhead history, as its name implies, is to create a fictional new historical world based on a small amount of historical data. As for overhead history, many people think that it is an event that people (or others) go from their own time and space (let's call it A time and space) to another time and space (call it B time and space) through a certain process (or no process) for some reason, usually in ancient times and different dynasties.
For example, the overhead historical novel "Floating Clouds".