"Tale of Heike," by anonymous, tells about the fall of Heike, the first clan of warriors that enjoyed strong power in Japan. The main theme of this tale is transience. Transience is one of the most important views of the world in Buddhism; it refers to the notion of the transmigration of souls, which hold that all souls certainly die and everything is certain to change. Therefore, this tale begins with a view of the world as transient.
However, I think this view of the world still holds true every time; for example, the overthrow of the Roman Empire and the Ching Dynasty, etc., which were strong nations.