The Battle of Aclea occurred in 851 between the West Saxons led by Æthelwulf, King of Wessex from 839 to what year, and the Danish Vikings?
Æthelwulf Æthelwulf (Old English for "Noble Wolf"; died 13 January 858) was King of Wessex from 839 to 858. In 825, his father, King Egbert, defeated King Beornwulf of Mercia, ending a long Mercian dominance over Anglo-Saxon England south of the Humber. Egbert sent Æthelwulf with an army to Kent, where he expelled the Mercian sub-king and was himself appointed sub-king. After 830, Egbert maintained good relations with Mercia, and this was continued by Æthelwulf when he became king in 839, the first son to succeed his father as West Saxon king since 641.
Æthelswith Æthelswith (c. 838–888) was the only known daughter of King Æthelwulf of Wessex. She became Queen Æthelswith when she married King Burgred of Mercia in 853. The couple had no issue. Her marriage probably signalled the subordination of Burgred to his father-in-law and the Saxon kingdom at a time when both Wessex and Mercia were suffering Danish (Viking) raids. Burgred also had ongoing problems with the Kingdom of Powys on his western border and in 853 Æthelwulf subjugated the Welsh state on Burgred's behalf.