After World War I, the colonial territories of the defeated powers were distributed to the victorious allies, under the general supervision of the League of Nations. It was a system of trusteeships established by Article 22 of the Covenant of the League of Nations for the administration of former Turkish territories and of former German colonies. As finally adopted, the mandates system marked an important innovation in international law with respect to the treatment of dependent territories. A mandated territory differed from a protectorate in that obligations were assumed by the mandate power to the inhabitants of the territory and to the League, which supervised mandates. It differed from a sphere of influence in that the guardians had an acknowledged right to raise and expend revenues, to appoint officials, and to make and enforce laws. The mandate system was administered by the League of Nations through a Permanent Mandates Commission of 11 members.

The mandated territories were divided into three classes based on their economic, political development and their location, and were then assigned to individual powers. Class A consisted of Iraq (British), Syria and Lebanon (French), and Palestine (British). The provisional independence of these former Turkish provinces was recognized, subject to administrative control until they could stand alone. By 1949 all former Class A mandates had reached full independence. Class B was composed of the former German African colonies, South West Africa excepted—Tanganyika and parts of Togoland and the Cameroons (British), Ruanda-Urundi (Belgian), and the greater part of Togoland and the Cameroons (French). The establishment of military or naval bases in these regions by the mandatories was forbidden; commercial equality with other nations and native rights were guaranteed.

Class C territories were South West Africa (South Africa), former German Samoa (New Zealand), New Guinea (Australia), Nauru (Australia), and former German islands in the Pacific, north of the equator (Japan). While fortification of these mandates was forbidden and native rights were guaranteed, these areas were to be administered by the mandatories as integral parts of their empires.

With the creation of the United Nations, the mandates system was superseded by the trusteeship system. All remaining mandated territories became trust territories except South West Africa (now Namibia), whose status was contested by South Africa and the United Nations until it became independent in 1990.