Harald the younger had been exiled from Denmark and had raided Frisia for several years. He had entered an alliance with Lothair I who was involved in conflict against Louis the Pious, his father. Frisia was part of Louis' lands and the raids were meant to weaken him. By 841, Louis was dead and Lothair was able to grant Harald and Rorik several parts of Friesland. His goal at the time was to establish the military presence of his loyalists in Frisia, securing it against his siblings and political rivals Louis the German and Charles the Bald. The two Norsemen used islands as a main base of operations, the seat of Rorik being the island of Wieringen, while Harald operated from the island of Walcheren, and they also ruled Dorestad at this time.