865-871: The 'Great Heathen Army' (The Reign of Ethelred of Wessex)

The Danish forward base in Thanet has, until now, been essentially a smash-and-grab and extortion racket. The Saxons in Kent, for example, get peace but only if they pay protection money and the Danes have no intention of honouring any agreements if they can get away with it. The real action, presenting an existential threat to England, is about to take place a little to the north as organised crime shifts into its political mode, a war of conquest.

In 865 a Danish 'Heathen Army', an invasion force possibly seeking land but certainly seeking tribute, appears under the command of Halfdan Ragnarrson and Ivar the Boneless, said to be sons of the legendary Norse King Ragnar Lodbrok (if he actually existed which is a matter that is up for historical grabs). It moves across England in the following year, taking control of York in 865 and ravaging Mercia and Northumbria. King Aelle of Northumbria and his rival Osberht are both killed in battle (the rivals united to meet a common threat) and replaced by a Viking puppet Egbert I.

Ethelred moves to try and dislodge the Vikings from Nottingham in 868, accompanied by Alfred who had married Elswitha of Mercia in the previous year but little progress is made. The 'Great Heathen Army' moves back down into East Anglia in 869, murdering Edmund King of East Anglia (his successor is Oswald, the last King of East Anglia) in 870 when he declines to play the same role there as Egbert in Northumbria.

The strategy of permanent tribute and conquest seems to be targeted at the whole of England. As winter draws close in 870, the Danes (Danes, Norse, Heathens and Vikings are interchangeable terms in this context) move south into the Thames Valley as far as Reading, right up to the borders of the Wessex heartland. In a major battle at Ashdown in 871, Ethelred and Alfred lead a Saxon army in a major victory over the invaders under Halfdan and Bagsac. Ethelred is severely injured and dies and is succeeded by Alfred. As he comes to the throne, the Danish invaders have been checked by the strongest remaining Anglo-Saxon Kingdom, one about to become England itself, but they are far from defeated. It is down to Alfred to become 'the Great' in containing the threat over the next couple of decades.