Ethelred the Pious
The Kingdom of Kernow, or Cornwall, emerged in the Sixth Century as a breakaway state or sub-kingdom of the Kingdom of Dumnonia. The Saxons called it "West Wales". By the late Ninth Century the kingdom was coming under the dominion of Wessex, and much of its land was owned by West Saxon priests. The gradual Saxon takeover of the little country was halted by the Vikings' conquest of England in the 870s.
By the 890s, neither Kernow nor England's southwest were yet under the control of the new ruler, the King of Jorvik. In 904 King Hogni invited Hrolfr the Northman, a Danish chieftain, to settle in the country of Dafna and subdue it for Jorvik. Dafna (Devon) was just across Kernow's eastern border.
Hrolfr made quick work in conquering his new jarldom, and soon was looking to expand his personal power. In 904 he led an army into Kernow. Rather than simply add Kernow to his jarldom, Hrolfr saw the value in allowing it to remain totally separate from Jorvik. He placed his 11-year-old son Viljhalmr, or William, on the Cornish throne.
In 924, Hrolfr backed a losing candidate for the throne of Jorvik. Thereafter he steadily lost influence in England and concentrated more on his Cornish kingdom. Vilhjalmer continued these policies after his father's death. In the 930s, he began his own journeys of expansion, adding the isles of Adreney, Wernsey, and Jarsey to his kingdom, then landing on mainland Europe to take the fortress of Carsborg. In order to maintain his independence, William often had to play along with foreign powers and accept vassalage to them: this he did with Jorvik in the 940s and Erik the Mariner, ruling from Ostangeln, in the 950s.
Vilhjalmr died in 960. His son was known only by his Cornish name, Donyarth II. Like his father, he was a Christian and was quite integrated into Cornish culture - even more so since by the time he assumed the throne, his family's title in England was being challenged, and other nobles had seized control of much of Dafna. Donyarth maintained the Cornish kingdom on both sides of the Channel. During his reign, the Channel Islands were settled with Cornish farmers. He had to fight several times to defend Carsborg and its peninsula against incursions from both Angelania and Neustria.
Around 980 Donyarth made an alliance with Guy I of Neustria. The two kings agreed to help each other: Cornish ships would help with Guy's war in Brittany, while Neustrian money would help pay for defense against Angelanian raiders. Donyarth transferred his feudal allegiance from Ostangeln to Neustria, and Guy agreed to let him keep Carsborg.
The Danes under Sweyn Forkbeard conquered and united England around 1000. Sweyn accepted Kernow's capitulation but made no effort to conquer it outright. So Kernow's status continued as it had since Saxon times: it was a semi-independent kingdom under the suzerainty of yet another powerful neighbor. King Cnut confirmed Kernow's status when he came to power in 1018. By then, the nobles of southern England were finally taking an interest in Cornish land and were beginning to encroach on its border. Madron, Kernow's king during the time of Cnut, began to look for outside allies.