What if St. Edwin was not killed at the battle of Hatfield Chase, but instead was victorious?
According to Wiki, Edwin was Bretwalda, and recognized as over-lord by all the Anglo-Saxons except Eadbald of Kent.
He already had control of Northern England, Anglesey and Gwynedd.
At Hatfield chase, he was defeated by the exiled King of Gwynedd and Penda of Mercia, would it be possible, then, if he wins to add Mercia to his Northumbrian kingdom?