Æthelflæd, Lady of the Mercians (c. 870 – 12 June 918) ruled Mercia in the English Midlands from 911 until her death. She was the eldest daughter of Alfred the Great, king of the Anglo-Saxon kingdom of Wessex, and his wife Ealhswith. Æthelflæd was born around 870 at the height of the Viking invasions of England. By 878 most of England was under Danish Viking rule, East Anglia and Northumbria having been conquered, and Mercia partitioned between the English and the Vikings, but in that year Alfred won a crucial victory at the Battle of Edington. Soon afterwards the English-controlled western half of Mercia came under the rule of Æthelred, Lord of the Mercians, who accepted Alfred's overlordship. Alfred adopted the title King of the English, claiming to rule all English people not living in areas under Viking control. In the mid-880s, Alfred sealed the strategic alliance between the surviving English kingdoms by marrying Æthelflæd to Æthelred.
Æthelred played a major role in fighting off renewed Viking attacks in the 890s, together with Æthelflæd's brother, the future King Edward the Elder. Æthelred and Æthelflæd fortified Worcester, gave generous donations to Mercian churches and built a new minster in Gloucester. Æthelred's health probably declined early in the next decade, after which it is likely that Æthelflæd was mainly responsible for the government of Mercia. Edward had succeeded as King of the Anglo-Saxons in 899, and in 909 he sent a West Saxon and Mercian force to raid the northern Danelaw. They returned with the remains of the royal Northumbrian saint, Oswald, which were translated to the new Gloucester minster. Æthelred died in 911 and Æthelflæd then ruled Mercia as Lady of the Mercians. The accession of a female ruler in Mercia is described by the historian Ian Walker as "one of the most unique events in early medieval history".
Alfred had built a network of fortified burhs and in the 910s Edward and Æthelflæd embarked on a programme of extending them. Among the towns where she built defences were Bridgnorth, Tamworth, Stafford, Warwick, Chirbury and Runcorn. In 917 she sent an army to capture Derby, the first of the Five Boroughs of the Danelaw to fall to the English, a victory described by Tim Clarkson as "her greatest triumph". In 918 Leicester surrendered without a fight. 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 ... I 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.
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 situation was transformed the following year when Alfred won a decisive victory over the Danes at the Battle of Edington.
Ceolwulf is not recorded after 879. His successor as the ruler of the English western half of Mercia, Æthelflæd's husband Æthelred, is first seen in 881 when, according to the historian of medieval Wales, Thomas Charles-Edwards, he led an unsuccessful Mercian invasion of the north Welsh Kingdom of Gwynedd. In 883 he made a grant with the consent of King Alfred, thus acknowledging Alfred's lordship. In 886 Alfred occupied the Mercian town of London, which had been in Viking hands. He then received the submission of all English not under Viking control and handed control of London over to Æthelred. In the 890s, Æthelred and Edward, Alfred's son and future successor, fought off more Viking attacks. Alfred died in 899 and Edward's claim to the throne was disputed by Æthelwold, son of Alfred's elder brother. Æthelwold joined forces with the Vikings when he was unable to get sufficient support in Wessex, and his rebellion only ended with his death in battle in December 902.