I'm the Emperor From the Future

In the Great Han, the throne is a seat somebody else usually controls. The Empress Dowager rules through whoever sits on it, the vassal kings hold their own territory and armies, and the great clans arrange the rest. Leonard wakes up in the body of the emperor. He has the knowledge of a much later century and no patience, and he uses both. He puts down revolts inside the borders, takes apart the plots run by the Xiao family and Prince Quentin, and turns back the Xiongnu on the frontier. Steam engines and modern military tactics come out of his head and into the field. Power collects around him a piece at a time, and he ends by purging the court of everyone who worked against him.