Shortly afterwards the Viking leaders of York offered her their loyalty, but she died on 12June 918 before she could take advantage of the offer, and a few months later Edward completed the conquest of Mercia. Æthelflæd was succeeded by her daughter Ælfwynn, but in December Edward took personal control of Mercia and carried Ælfwynn off to Wessex. Historians disagree whether Mercia was an independent kingdom under Æthelred and Æthelflæd but they agree that Æthelflæd was a great ruler who played an important part in the conquest of the Danelaw. She was praised by Anglo-Norman chroniclers such as William of Malmesbury, who described her as "a powerful accession to [Edward's] party, the delight of his subjects, the dread of his enemies, a woman of enlarged soul". According to Pauline Stafford, "like ... ElizabethI she became a wonder to later ages". In Nick Higham's view, medieval and modern writers have been so captivated by her that Edward's reputation has suffered unfairly in comparison. Background Mercia was the dominant kingdom in southern England in the eighth century and maintained its position until it suffered a decisive defeat by Wessex at the Battle of Ellandun in 825. Thereafter the two kingdoms became allies, which was to be an important factor in English resistance to the Vikings. In 865 the Viking Great Heathen Army landed in East Anglia and used this as a starting point for an invasion. The East Anglians were forced to buy peace and the following year the Vikings invaded Northumbria, where they appointed a puppet king in 867. They then moved on Mercia, where they spent the winter of 867–868. King Burgred of Mercia was joined by King Æthelred of Wessex and his brother, the future King Alfred, for a combined attack on the Vikings, who refused an engagement; in the end the Mercians bought peace with them. The following year, the Vikings conquered East Anglia. In 874 the Vikings expelled King Burgred and Ceolwulf became the last King of Mercia with their support. In 877 the Vikings partitioned Mercia, taking the eastern regions for themselves and allowing Ceolwulf to keep the western ones. He was described by the Anglo-Saxon Chronicle as "a foolish king's thegn" who was a puppet of the Vikings. The historian Ann Williams regards this view as partial and distorted, that he was accepted as a true king by the Mercians and by King Alfred. The