In 1660, the Dutch recognised the Sultan of Tidore's sovereignty over New Guinea. New Guinea thus became notionally Dutch as the Dutch held power over Tidore. In 1793, Britain established a settlement near Manokwari. However, it failed. By 1824 Britain and the Netherlands agreed that the western half of the island would become part of the Dutch East Indies. In 1828 the Dutch established the settlement of Fort Du Bus at Lobo (near Kaimana), which also failed. Great Britain and Germany had recognised the Dutch claims on western New Guinea in treaties of 1885 and 1895. Dutch activity in the region remained minimal in the first half of the twentieth century. Dutch, US, and Japanese mining companies explored the area's rich oil reserves in the 1930s. In 1942, the northern coast of West New Guinea and the nearby islands were occupied by Japan. In 1944, Allied forces gained control of the region through a four-phase campaign from neighbouring Papua New Guinea. The United States constructed a headquarters for MacArthur at Hollandia (Jayapura), intended as a staging point for operations to retake the Philippines. Papuan men and resources were used to support the Allied war effort in the Pacific. After the war's end, the Dutch regained possession of the region.