In the 8th century, under kings Aethelbald and Offa, Mercia became the dominant Saxon Kingdom, extending their overlordship to the Channel coast. Egbert, who became king of Wessex in 802, maintained a fraught independence for two decades while the bellicose Mercian ruler Coenwulf focussed his aggression on Kent, East Anglia and Wales. After Coenwulf’s death, a period of instability ensued, and Egbert, seizing his opportunity, decisively defeated the Mercians at Ellendun (825). Egbert lacked the military resources to immediately exploit his advantage, but after two Mercian kings were slain in quick succession by East Anglian rebels, he again seized the moment to ravage Mercia and southern Northumbria, forcing the Northumbrian king to pay tribute to him. By then, Egbert had annexed the old kingdoms of Sussex, Essex and Kent, and imposed his authority over Cornwall. Mercia rapidly regained its independence, and by the end of his reign, Egbert was facing Danish incursions in the west.
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