Complex sentence: Oswiu offered him a great ransom of treasure which, according to Bede, was refused (or according to the Historia Brittonum, was accepted and distributed)--in either case Penda resolved on battle and the destruction of the Northumbrians.
Split into simpler sentences: Oswiu offered him a great ransom of treasure which, according to Bede, was refused (or according to the Historia Brittonum, was accepted and distributed). In either case Penda resolved on battle and the destruction of the Northumbrians.