According to Vietnamese feudal historians, the establishment of the Yuan dynasty was very complex. First, the Yuan dynasty was seen as being as powerful as the Song dynasty. And, it did control the entirety of China from a certain time until 1368. Vietnamese historians of the feudal era did not agree about when the Yuan dynasty was established. Some said that God played an important role in the dec1ine of the Song dynasty. Others thought that politics, economics, and military strength might have had something to do with why the Yuan dynasty came into power.