While Alfred the Great was highly effective in his rule it is important to recognise that he was King first and foremost of Wessex, one of the major Anglo-Saxon kingdoms of the day, and the identity of England as a unified feudal kingdom had not yet been established. Alfred is often regarded as ‘King of the Anglo Saxons’, reinforcing that despite his reputation in Britain, England was not a culturally or ethnically homogenous domain. Additionally, while Alfred’s successes against the Sons of Ragnar as well as invaders from Denmark were significant, they did not immediately result in the destruction of the Viking controlled Northumbria or Deira (later York or Jórvík).

Alfred’s son and successor Edward the Elder made significant inroads into Nordic controlled Britain throughout his reign and had consolidated the Danish held territories in Mercia and East Anglia. By the end of Edward’s reign only King Sihtric of York remained as a Viking lord of significance in the traditionally Anglo Saxon territories.

Æthelstan, upon his ascension to the throne in 924, moved efficiently to take control of the Viking Kingdom. Firstly, the establishment of peaceful diplomatic and familial relations via the marriage of Edith of Polesworth (tenuously considered to be Æthelstan’s sister) to King Sihtric, rendering peace temporarily between the two kingdoms. Subsequently, following Sihtric’s death in 927, Æthelstan moved quickly to invade York, accepting the submission of the Danish people and expunging the Viking identity from the ruling class of the Anglo Saxon world. Furthermore and at approximately the same time as Æthelstan’s invasion of York, the ambitious king easily repelled an invasion from Dublin led by Gunfirth, a cousin of Sihtric, which further solidified his position at the helm of the Anglo Saxon lands and their people.

While initially Æthelstan’s rulership in the north of England was met with outrage by native Northumbrians, who had traditionally rejected southern control with vigour, he quickly strengthened his position in the region. The acceptance of Æthelstan’s overlordship by King Hywel Dda of Deheubarth, Ealdred of Bamburgh (a ruler of Bernicia in northern Northumbria), King Owain of Strathclyde and King Constantine II of Alba at Eamont in 927 safeguarded his local rule and instigated 7 years of unprecedented peace in England’s north. Historian John Maddicott describes Æthelstan’s rule as the beginning of ‘the imperial phase’ of English kingship; a period in which the British rulers in Wales and Scotland attended the courts of English kings, took part in their assemblies and recognised their charters. And while Æthelstan’s popularity and efficacy of rule in the north was diminished as his reign progressed, he managed to maintain the lands he had come to rule.

Essentially Æthelstan was the first ‘southern’ king to take the mantle of ruler in the regions of York and Northumbria, thereby becoming the first to rule over a territory comparative to what we today consider to be England.

For the simple reason that Alfred never unified England during his reign. While he managed some level of nominal overlordship over Mercia, at the time of Alfred's death, Mercia was still very much an independent political entity, and would remain so until the 920s. The English kingdoms also wouldn't really begin their advance into the Danelaw territories in earnest until the reign of Edward the Elder in Wessex.

When Æthelstan came to the throne in 924/5, his succession was far from straightforward, but he was in fact elected king in Mercia before he gained the throne of Wessex, and then received the submission of Northumbria after his victory at Brunanburh.