|King William II|
The failure of either of these royal brethren to defend their subjects' rights adequately was the reason John Uskglass gave for invading Northern England. He claimed that both he and his father had suffered at the hands of an enemy, Hubert de Cotentin, without either king attempting to avenge their wrongs or restore them to their lands. The rightness of his cause seemed clear to him: and it is of course true that the feudal bond was based on mutual obligation, and that a vassal swore fealty on the expectation that his lord would give him protection and justice. Nevertheless John Uskglass's decision to seize lands much beyond what he could ever have inherited, while at the same time casting off all duty to his Christian overlord, is remarkable in its boldness.
Of course, other historians have argued that the right of Duke William of Normandy and his successors to the throne of England was also itself of dubious legality. It is perhaps best to accept that, in those turbulent times, might was generally right.