King Ine and Offa of Mercia
From 'A History of the British Nation' by AD Innes, 1912
England during this century [7th century] achieved a foremost place as a home of learning and culture. During its first half flourished the Venerable Bede, the most learned man of his time, historian, scholar, and saint; and about the year of his death was born Alcuin, who in matters intellectual became the chosen counsellor of the mighty emperor whom we call Charlemagne. But England was not a happy realm; because nowhere within its borders was to be found a dominion with a strong central government organised on a permanent basis.
The different kingdoms were in rivalry with each other, besides being perpetually rent by civil broils, from the absence of any fixed law of succession except that which required that the king should be of the blood royal. There was occasionally a strong and capable king in one or other of the greater kingdoms whose reign is marked by the expansion of his own realm.
Ine of Wessex
Thus, about the beginning of the eighth century, Ine of Wessex drove the Celtic boundary in the southern peninsula fairly back into Devon. This king is also celebrated for that codification of the customs of Wessex known as the Dooms or Laws of Ine. Mercia had remained on terms of what may be called mutual toleration with Northumbria, but after Ine's death AEthelbald of Mercia challenged the temporary Wessex supremacy in the south, and made himself supreme from the English Channel to the Humber. Turning to the north he tried but failed to master Northumbria, which was still strong enough to defend itself, though not to retaliate upon the southern dominion.
Then Mercia itself began to fail to pieces even before the old King AEthelbald was himself assassinated; but its power was restored by the great King Offa, who shortly afterwards seized the throne, and, after setting the affairs of Mercia in order, proceeded to make himself supreme in England.
Offa's reign began in 758 and lasted till 796. He drove Wessex back south of the line of the Thames and Severn mouth and pressed the Welsh back far west of the Severn, marking the new boundary between Britons and English by the great line of Offa's Dyke from Chester to the Bristol Channel. Europe recognised him as the lord of England, and he treated as an equal with Charles the Great, King of the Franks, who had not yet revived the Western Empire and assumed the Imperial crown. But apparently he did not care to trouble himself with the subjection of Northumbria, which, throughout his reign, was in a state of miserable chaos, a term which also applies generally to the Pictish and Scottish dominions and to Strathclyde with its diverse population of Gaels and Britons.
The arrival of the Danes
The last years of Offa saw the first attack upon the English shores by a new enemy, the Danes or Northmen from over the sea, whose appearance marks the arrival of the third stage of our history after the Roman evacuation.