In 1066, William, the Duke of Normandy, took advantage of the English succession crisis to start the Norman Conquest. With an army of Norman followers and mercenaries, he defeated Harold at the battle of Hastings and rapidly occupied the south of England. William used a network of castles to control the major centres of power, granting extensive lands to his main Norman followers and co-opting or eliminating the former Anglo-Saxon elite. Major revolts followed, which William suppressed before intervening in the north-east of England, establishing Norman control of York and devastating the region. Some Norman lords used England as a launching point for attacks into South and North Wales, spreading up the valleys to create new Marcher territories. By the time of William's death in 1087, England formed the largest part of an Anglo-Norman empire, ruled over by a network of nobles with landholdings across England, Normandy, and Wales. England's growing wealth was critical in allowing the Norman kings to project power across the region, including funding campaigns along the frontiers of Normandy.