The Americans built schools and other buildings and instituted changes in the overall political system. However, the province's economy remained particularly agricultural with rice replacing corn and tobacco as the dominant crop. World War II stagnated the province's economic growth but it recovered dramatically after the war. In 1942, Imperial Japanese occupied Isabela. In 1945, the liberation of Isabela commenced with the arrival of the Philippine Commonwealth troops under the Philippine Army, Constabulary, and USAFIP-NL units and recognized guerrillas attacked by the Japanese Imperial forces in World War II.