The Northumbrian Revolt of 1065 was a rebellion in the last months of the reign of Edward the Confessor against the earl of Northumbria, Tostig Godwinson, brother of Harold Godwinson, Earl of Wessex. Tostig, who had been earl since 1055, is said to have provoked his nobles to rise against him by his harsh administration of justice, raising of tax levels, frequent absences from his earldom, and murder of several political opponents. In October 1065 the rebels entered Northumbria's capital, York, killed Tostig's men, looted his treasury, renounced their allegiance to Tostig and proclaimed Morcar, brother of Edwin, Earl of Mercia, as their new earl. They then marched south to Northampton, causing much devastation in Yorkshire and the north Midlands as they went, and joining forces with the army of Mercia. The king sent his chief earl, Harold Godwinson, to negotiate with them, and when they refused to compromise on the deposition of Tostig he tried and failed to raise his own army against them. On Harold's advice, he finally gave in to their demands and recognised Morcar. Tostig was sent into exile in Flanders, from where, disgusted at what he saw as his brother's betrayal, he shortly afterward raided the English coast, finally dying in arms against him at the Battle of Stamford Bridge.
The Northumbrian Revolt was seen at the time, and is still often seen, as the first stage in the destabilising of the English kingdom that led up to the Norman Conquest.
Background
During the first part of the reign of Edward the Confessor, from 1042 to 1055, much of his power was shared with his nobles, of whom the most important were the earls of Wessex, Mercia and Northumbria. By the end of this period there was a balance of power between the three main noble families, Harold Godwinson controlling the south of England, Siward the north, and Leofric and his son Ælfgar the centre.
This state of affairs came to an end when Siward, Earl of Northumbria died in 1055, presenting Edward with a difficult choice of successor. Siward's elder son had already died in battle, and the younger one was still a child, so the successful candidate would have to come from a different family. He would need to be able to win the support of the Northumbrian nobles, but also work closely with Edward himself and help to integrate this distant earldom into the larger English political structure. Leofric's son Ælfgar, Earl of East Anglia, seems to have been hopeful that he would win the prize, and possibly some unknown member of the ancient ruling house of Bernicia had the same ambition, while Harold, Earl of Wessex, was lobbying for his younger brother, Tostig. When the king's council, the Witan, was convened on 19 March, Ælfgar was taken out of the running by being accused of treason and sentenced to outlawry, and Northumbria was assigned to Tostig. Ælfgar was soon reinstated in East Anglia, and when his father died in 1057 he was allowed to succeed him in Mercia, though Gyrth, another of the Godwinsons, became Earl of East Anglia in his stead. This move, together with the creation of new minor earldoms and substantial redrawing of borders at Ælfgar's expense, left him possessed of a smaller Mercia than his father had ruled, while all the rest of England was held, under the king, by the Godwinsons, and principally by the brothers Harold and Tostig.
Tostig's rule in Northumbria
The Vita Ædwardi Regis, an anonymous Latin life of Edward the Confessor written at about the time of the Norman Conquest, includes a description of Tostig's appearance and character. It calls him strong, brave, handsome and graceful, open-handed, especially with gifts to the Church, trustworthy, faithful to his wife, secretive, shrewd, not rash, capable of restraint, but generally vigorous and unwearying in pursuing his purposes, sometimes to the point of overzealousness in confronting evil. He was a particular favourite with the king. When he took up his new position he was probably still in his mid-twenties, and the task that faced him was formidable. Northumbria was a turbulent, feud-ridden, and lawless province far distant from his own native Wessex, and its nobles may have resented having a southerner placed over them, though it is also possible that having no connection with any of the three main Northumbrian factions (based around the house of Bamburgh, the see of Durham, and the Yorkshire nobility) he benefited from being seen as neutral. Perhaps also the fact that Tostig had a Danish mother would have helped him to understand the mixed Anglo-Saxon and Danish culture of Northumbria.