Nicholas Brooks noted that "the Mercians stand out as by far the most successful of the various early Anglo-Saxon peoples until the later ninth century", and some historians, such as Sir Frank Stenton, believe the unification of England south of the Humber estuary was achieved during the reign of Offa.
Nicholas Brooks observou que "os merciáns destacan de lonxe como o máis exitoso dos diversos primeiros pobos anglosaxóns ata finais do século noveno", e algúns historiadores, como Sir Frank Stenton, creen que a unificación de Inglaterra ao sur do estuario do Humber logrouse durante o reinado de Offa.