After Oswald's defeat and death at the hands of Penda in 642 Bernicia fell to his brother Oswio, while Oswine son of Osric became king in Deira, though probably subject to Oswio.
The districts north of the Humber contained two kingdoms, Bernicia (q.v.) and Deira, which were eventually united in Northumbria.
At his death in 633 the kingdom was again divided, Deira falling to his nephew Osric, while Bernicia was occupied by Eanfrith son of ZEthelfrith.
Originally it comprised two independent kingdoms, Bernicia and Deira.