Wulfstan's career is characterised by frequent swapping of allegiances, both among Viking leaders from Dublin and the Wessex kings. Perhaps Wulfstan played the part of 'king-maker' in Northumbrian politics in the mid-10th century, or perhaps he was guided by self-preservation and the interests of the Church in Northumbria. In 939, King
Olaf Guthfrithson of
Dublin invaded Northumbria and occupied
York. King
Edmund of England marched north to remove Olaf from York, but in 940 Wulfstan and Archbishop
Wulfhelm of Canterbury arranged a treaty that ceded the area between
Watling Street and the border of Northumbria to Olaf. But Olaf died in late 940, and his rule in York was inherited by his cousin,
Olaf Sitricson who became King of
Jórvík. In 944, Olaf Sitricson and his co-ruler Ragnald Guthfrithson were driven out from York; the chronicler
Æthelweard wrote that it was "Bishop Wulfstan and the eoldormen of the Mercians" who were responsible for their expulsion. In 947 Wulfstan invited
Eric Bloodaxe, the
King of Orkney to become King of Jórvík.
Eadred of Wessex brutally ravaged Northumbria in 948, forcing Eric to leave Northumbria. Olaf Cuaran then resumed his second reign at York. By 951, Wulfstan appears to have supported Eric's claim to the kingdom of York over Olaf as he ceased to witness charters at the English court. In 952, Olaf was driven out by the Northumbrians in favor of Eric. ==Later life==