We look at Alfred the Great and how Wessex survives the Viking invasions from 870-878.
The History of England
In 870 the Great Heathen Army turns its attention to Wessex. The first campaign of 871 sees 9 battles fought, and Alfred the Great suceed his brother Athelred to the throne of Wessex. Although Wessex wins the battle of Ashdown, it has little overall impact, and Alfred is defeated at Basing, Wilton, and Maredun. In the end, Alfred pays the Vikings to go away, and the they have been to fight so hard that they agree.
But they are back in 878, and reduce Alfred to his closest thegns in the marsh at Athelney. In his famous fightback, Alfred rebuilds Anglo Saxon confidence with a series of raids; pulls together the fyrds of Somerset, Wiltshsire and Hampshire and defeats the Vikings in a decisive battle at Ethandun.
There's a slightly odd bit of treaty that survives between Alfred and Guthrum. It does help us understand the division of lands - but spends most of its time demonstrating that Dane and Anglo Saxon are of equal value before the law.