The term heptarchy is sometimes used to imply a between the kingdoms that did not exist. From the 6th century to the 9th century these were simply seven kingdoms set up by the Germanic invaders and their descendants. There was little equality between them. Northumbria, Mercia and Wessex were the most powerful of the seven and often dominated the others. The kingdoms were gradually reduced in number. The heptarchy basically ended with the coming of the Vikings. The term heptarchy was popular among scholars from the 16th to the 19th centuries but is occasionally used today.