Mercian Supremacy

Sir Frank Stenton apparently coined the phrase, arguing that Offa of Mercia, who ruled 757–796, effectively achieved the unification of England south of the Humber estuary.

[2] Scholastic opinion on the relationship between the kingdoms of Wessex and Mercia at this time remains divided.

While the precise period during which the Mercian Supremacy existed remains uncertain – depending upon whether one includes the reigns of Penda (c. 626–655) and Wulfhere (658–675) – the end of the era is generally agreed to be around 825, following the defeat of King Beornwulf at the Battle of Ellandun (near present-day Swindon).

[3] Recorded by Bede as the nemesis of early Anglo-Saxon Northumbria, Penda of Mercia achieved an early expansion of his kingdom's territory, but his reign ended with his death in battle, which was followed by a brief three-year period when Northumbria ruled over the Mercians.

Some historians have suggested that Offa's defeat of the Welsh and the West Saxons of Wessex established the Mercian Supremacy, which remained unchallenged until 825 when Egbert of Wessex supported an East Anglian rebellion against Beornwulf of Mercia, whose defeat at Ellendun effectively brought the Supremacy to an end.