MacArthur's Allied forces landed on the island of Leyte on 20 October 1944, accompanied by Osmeña, who had succeeded to the commonwealth presidency upon the death of Quezon on 1 August 1944. Landings then followed on the island of Mindoro and around Lingayen Gulf on the west side of Luzon, and the push toward Manila was initiated. The Commonwealth of the Philippines was restored. Fighting was fierce, particularly in the mountains of northern Luzon, where Japanese troops had retreated, and in Manila, where they put up a last-ditch resistance. The Philippine Commonwealth troops and the recognized guerrilla fighter units rose up everywhere for the final offensive. Filipino guerrillas also played a large role during the liberation. One guerrilla unit came to substitute for a regularly constituted American division, and other guerrilla forces of battalion and regimental size supplemented the efforts of the U.S. Army units. Moreover, the cooperative Filipino population eased the problems of supply, construction and civil administration and furthermore eased the task of Allied forces in recapturing the country.