An Empire consist of multiple Kingdoms and an Emperor or Empress to rule over them. The ruler usually has his or her own Kingdom and then other Kingdoms that are Bannermen to him or her. From there those Kingdoms sometimes have Towns who are Bannermen to them. A great example of this would be Varamore of the Draconic Islands. Like how Prince and Princess are children of King and Queen, in the series, Duke and Duchess are children of Emperor and Empress.