Oswiu’s reign started, and continued, under great pressure.

Such was the power ascribed to Oswald’s mortal remains that his younger brother essayed a dangerous raid deep into the heart of Mercian territory to reclaim them. Oswiu must have ridden fast and hard, faster than the news of his passage, to Oswestry in Shropshire, passing through much Mercian territory, where he found Oswald’s arms and head impaled upon stakes before the tree that became known as Oswald’s tree (hence Oswestry).

Riding even faster north, Oswiu and his band of riders made their escape back to Northumbria, carrying his brother’s remains with them.

The kingdom had split back into its two constituent parts, with a son of the Deiran royal house, Oswine, ruling from York. To bolster his claims to Northumbria, Oswiu took as wife Eanflæd, the daughter of King Edwin, no doubt hoping that that would give him greater claim over the southern half of the kingdom. It didn’t.

In the end, Oswiu reunited his kingdom by treachery and assassination. He raised an army to confront Oswine who, seeing that his own forces were seriously outnumbered, withdrew and dispersed his army, deciding not to seek confrontation. But Oswine made the mistake of taking shelter in the hall of a man he had hitherto seen as his most trusted lieutenant, only to be betrayed and killed. Although Bede was appalled by the treachery, it is perhaps not so surprising from the viewpoint of the man who betrayed Oswine. The lord he had sworn service to had backed down in the face of aggression; it was not hard to see which way the winds of power were blowing. In such a case, it would be easy for the friend to think himself betrayed by his own lord, thus giving his conscience clearance to present his new king with the head of his enemy and curry his favour.