Deira was invaded by Aethelfrith of Bernicia in about the year 604. Aethelric was defeated and probably killed, and thereafter Aethelfrith ruled Deira and Bernicia together as Northumbria.
Bernicia was again separate from Deira under Eanfrith, son of Aethelfrith (633?634), after which date the kings of Bernicia were supreme in Northumbria, though for a short time under Oswiu Deira had a king of its own.
He invaded Deira in 651, and slew Oswine, after whose death he ruled all Northumbria (651 - 70), and gained supremacy over all Mercia, the South Angles, East Angles, and East Saxons, as well as many Britons and Scots, He was the 7th Bretwalda of the Anglo - Saxon Chronicle.
Deira (from Brythonic "Deifr", meaning "waters" and pronounced Deywr in the Celtic tongue) was a kingdom in England during the 6th century AD.