This isolation of the West Welsh, as the English thenceforth called them, largely broke the power of the native resistance.

Step by step in the succeeding age the West Saxons advanced by hard fighting, but with no serious difficulty, to the Axe, to the Parret, to the Tone, to the Exe, to the Tamar, till at last the West Welsh, confined to the peninsula of Cornwall, became known merely as the Cornish men, and in the reign of AEthelstan were finally subjugated by the English, though still retaining their own language and national existence.

But in all the western regions the Celtic population was certainly spared to a far greater extent than in the east; and the position of the English might rather be described as an occupation than as a settlement in the strict sense of the word.
The westward progress of the Northumbrians is later and much more historical.

Theodoric, son of Ida, as we may perhaps infer from the old Welsh ballads, fought long and not always successfully with Urien of Strathclyde.

But in 592, says Baeda, who lived himself but three-quarters of a century later than the event he describes, "there reigned over the kingdom of the Northumbrians a most brave and ambitious king, AEthelfrith, who, more than all other nobles of the English, wasted the race of the Britons; for no one of our kings, no one of our chieftains, has rendered more of their lands either tributary to or an integral part of the English territories, whether by subjugating or expatriating the natives." In 606 AEthelfrith rounded the Peakland, now known as Derbyshire, and marched from the upper Trent upon the Roman city of Chester.