Mandated territory. After World War I ended in 1918, certain colonies and territories were taken from the defeated nations and placed under the administration of one or more of the victorious nations. These areas were called mandated territories. The League of Nations, a forerunner of the United Nations (UN), supervised the governing countries in the administration of the territories. The League expected the governing countries to improve living conditions in the territories, and to prepare the people for self-government.