After the battles of Ashdown, Basing, and Merton, a treaty was negotiated, Danegelt was paid to the Danes - literally a payment to the Danes in exchange for a promise to behave - and an uneasy peace reigned. Halfdan and his men went back to Northumbria to consolidate their gains and divide up the land. Ivor the Boneless after attacking East Anglia and murdering King Edmund had taken his loot and sailed with his army to Ireland. There he set up camp in a harbour town and declared himself king of Dublin. Guthrum emerged as overall leader of what was left of the great Viking army and was joined by new Vikings from the Danish homeland.
With Halfdan controlling the huge tracts of Northumbria and Mercia, East Anglia was already bursting at the seams when two more Viking chieftains Oscetel and Anund joined Guthrum in Cambridge. They combined forces and with Guthrum at the head moved against Wessex, taking and fortifying Wareham. The Saxon King, Alfred, placed the city under siege but was unable to winkle the Danes out and in the end had no choice, but to come to an agreement and buy the peace once more.
Guthrum - as was the Viking way - broke the agreement the following year and seized Exeter. Besieged by Alfred's army Guthrum called for reinforcements from the Viking fleet. Alfred however had built a small fleet of ships manned by mercenaries and he ordered his tiny fleet to intercept them. Luckily a great storm blew up and wrecked 120 ships belonging to the Viking fleet. With no hope of reinforcements Guthrum had little choice but to abandon the city and withdraw into Mercia.
The next year King Alfred raised a large army and marched on the Vikings who were now encamped at Exeter. Guthrum finding himself besieged fled north to Gloucester. The following winter, Guthrum after carrying out a surprise attack on Chippenham sent King Alfred himself fleeing into the marshes that surrounded Athelney. The Danes were now in control of Wessex and were not too troubled by Alfred's occasional guerrilla raids.
Guthram declared himself King of Wessex. But Alfred was not beaten yet; he raised men from Somerset, west Hampshire and Wiltshire. After clashing with the Danes at Countibury hill he then marched to Edington to confront Guthrum's main army. Alfred attacked at dawn, the fighting was fierce and lasted all day but in the end Guthrum's army broke and were pursued back to the base at Chippenham. Trapped for nearly three weeks in the Saxon King's own fortress without food and water, Guthrum has no choice, but to sue for peace.
Despite Guthrum being Alfred's prisoner, they agreed between them to split the country in two. Alfred's Wessex to the south of the old Roman road called Watling Street and the Danish, Danelaw to the east and north. Alfred however drove a hard bargain and Guthrum was forced to pledge Viking hostages to the king, without taking any himself. (Something he had never done before.) He also had to agree to become a Christian and retire with his army back to the Danish side of the border.
Guthrum and his army left and the main Viking force over wintered in Fulham. Later in the year Guthrum and thirty his men returned to Wessex and in a ceremony at the small church on the Isle of Aller was baptised into the Christian faith. With Alfred acting as his sponsor, Guthrum was Christened with a good Old Saxon name, that of Aethelstan. After 12 days of feasting the two leaders ratified the peace of Wedmore and the Danelaw came fully into force.
Guthrum - now called Aethestan - retired to his base in the east and on the death of the puppet King Aethelred of East Anglia, took the throne and ruled in peace until his death 10 years later.
