Well it was Wessex and Mercia combined which repulsed the Viking invasions in the 870s and 880s. Mercia suffered a severe setback following the Battle of Repton in 873, but contrary to what the Anglo-Saxon Chronicle would have us believe, Mercia was very much militarily active in the late 870s, and the relationship between Alfred of Wessex and Ceolwulf II was seeming a lot closer than the antagonistic one with a 'foolish king's thegn' puppet that the ASC portrays. In particular, the minting of 'Two Emperors' coinage in London - an emulation of a common-in-Britain Roman solidus design depicting Alfred and Ceolwulf reigning side by side - suggests that Alfred was willing to see the two as equals. Contemporary Welsh annals also suggest that Ceolwulf and a Mercian army was campaigning actively in Wales for the late 870s, perhaps as a means of shoring up Mercian territory in the wake of post-873 losses. Indeed, in 886, the refortified burh of London is entrusted to the Mercians, and in 893, a Mercian and Welsh contingent plays an important role in the victory over the Danish army at Buttington.

The burh system is central to the defence of Wessex and broadly speaking functions very effectively in limiting the Danish strategy of manoeuvre warfare and using hit-and-run tactics to bleed manpower reserves before a battle. Much is often made of the Danish attack on Chippenham in 878, but those accounts overlook that besides northwest Wiltshire, Wessex actually weathers the assault very well. At the same time as the Chippenham attack, the fyrd of the Devonshire burhs intercepts and destroys a Danish invasion, and purportedly captures the pop-culture famous 'Raven' banner. Indeed, Wiltshire, Somerset and Hampshire clearly considered themselves secure from attack, since the fyrds of these counties formed the basis of Alfred's victorious army at Edington. We also see the burh system functioning perfectly again in 911, when the combined Mercian fyrds under Æthelred defeat a major Danish-Northumbrian invasion of Mercia while the West Saxon army is in East Anglia. In 894, the people of Chichester put to flight a Viking raiding force which had retreated into Sussex having previously tried to lay siege to the burh at Exeter.

The West Saxon record in particular is relatively good. An important caveat to note is of course that the majority of our information comes from two West Saxon sources - recensions A-C of the Anglo-Saxon Chronicle and Asser's Vita Ælfredi - that are often essentially Cerdicing hagiographies; on the whole, the ASC is relatively good in noting when things don't go the West Saxons' way, but it does have a tendency to overlook or even outright deny the contribution of non-Wessex forces in the defence and unification of England, even during Æthelflæd's Cerdicing rule of Mercia from the 880s - 918. Indeed, Æthelflæd goes as far as to institute her own national annal - known as the Mercian Register - to chronicle Mercian achievements in the unification of England in the 900s and 910s. From the late 870s onwards, however, the West Saxon record at least is relatively good. 877, 878, 882, 883, 885, 893, 894 and 895 all see West Saxon victories over the Danes, both in land campaigns and naval actions. The significant Danish occupation in the period - the Weald in 892 - is noted to succeed because the burh there was still under construction and not yet properly defended.

Even in 871, when the situation for Wessex is quite poor, the West Saxon battle record is still quite effective; the Anglo-Saxon Chronicle and Asser both note that while West Saxon forces are on the whole successful in battle, Wessex is not able to sustain the huge manpower drain of trying to secure its territory against 'countless' raids, alongside the nine major battles fought and the 'many' minor expeditions led by Æthelred and Alfred, and the Saxon reversals of that year come about as a result of their armies being frequently outnumbered by the Danes.

The Anglo-Saxon Chronicle is brief and blunt about the fall of Northumbria, but Asser is surprisingly charitable: in the Vita Ælfredi he notes that Northumbria was in the midst of great civil dispute when the Danes arrive, and accounts that the Northumbrians came close to putting the Danes to flight before they were surprised and overwhelmed, noting that York did not have such substantial fortifications it did at his time of writing. Asser also notes that Edmund of East Anglia fought 'fiercely' against the Danes, but was killed in battle, which led to the collapse of East Anglia in 870.