The description of King Sigeberht of Wessex being deposed by Cynewulf is notably fuller than earlier entries in the Anglo-Saxon Chronicle.

Sigeberht had succeeded his distant relative Cuthred in 756, but was then accused of acting unjustly.

He is removed from power by a council of nobles, but given control of Hampshire.

There, he is accused of murder, driven out and ultimately killed.

It is possible that this happened under the influence of Æthelbald of Mercia.

His brother Cyneheard is also driven out, but will return in 786 to kill Sigeberht's successor Cynewulf.

King Æthelbald is assassinated by his bodyguard in 757, and his cousin Offa, after a brief, successful civil war against Æthelbald’s murderers, becomes King of Mercia.

The conflict over the succession suggests that Offa needed to reestablish control over Mercia's traditional dependencies, such as the Hwicce and the Magonsæte.

Charters dating from the first two years of Offa's reign show the Hwiccan kings as reguli, or kinglets, under his authority; and it is likely that he was also quick to gain control over the Magonsæte, for whom there is no record after 740 of an independent rule.

Offa was probably able to exert control over the kingdom of Lindsey at an early date, as it appears that the independent dynasty of Lindsey had disappeared by this time.

Cynewulf is defeated by Offa of Mercia at the Battle of Bensington in 779; Offa then retakes Berkshire, and perhaps also London.

Despite this defeat, there is no evidence to suggest Cynewulf subsequently became subject to Offa (as his successor, Beorhtric, did).