League of Nations, international organization established at the Paris Peace Conference (1919) at the end of the First World War. It was founded on the principles of collective security and preservation of peace through arbitration of international disputes. American President Woodrow Wilson had taken an important part in founding the league, but the US never joined. Sixty-three states were eventually members. With headquarters in Geneva, Switzerland, it lasted until the founding of its successor, the United Nations, in 1945. Canada was a member throughout the league's existence, and served 192730 on the council.

The Covenant (the treaty provisions creating the league) established a council, assembly and secretariat. The council met quarterly and comprised the major powers as permanent members, plus non-permanent members elected by the assembly. The assembly consisted of representatives of all member states, and met annually. Under a secretary-general, the secretariat provided the permanent staff. A Canadian, Sir Herbert Ames, was financial director 191926, a high administrative position in the secretariat.

The league provided opportunities for international discussion of political and legal questions, disarmament, economic relations, the protection of minorities, communications and transit, and health and social questions. Members were required by Article 10 of the Covenant to respect and preserve each other's territory and independence. Aggression against any member would be considered aggression against all, and would lead to collective economic, and possibly military, measures. The purpose of collective security was to avert war, and in the 1920s the league participated in the attempted reconciliation of Germany with France and Great Britain. However, it proved incapable of effective action in the face of territorial aggression in the 1930s by Italy, Germany and Japan. The league ceased to function as a collective-security organization, although its social and economic activities continued until the Second World War.

From 1920 to 1923 the Canadian government actively but unsuccessfully sought removal of the collective-security guarantees, fearing involvement in European wars. More positively, in 1929, Raoul Dandurand, Canadian representative on the council, successfully proposed strengthening league procedures in overseeing the treatment of linguistic and religious minorities in eastern Europe. In 1935, when Canada supported the league's sanctions against Italy, Canadian delegate Walter A. Riddell proposed stopping all exports of oil, coal and steel to Italy. This action, unauthorized by the new Mackenzie King government, was publicly repudiated. Subsequently, Canada kept a low profile at league meetings.

The League of Nations, even though ultimately unsuccessful in achieving collective security, established a new pattern of international organizational activity. League membership brought Canada its first official contact with foreign governments, helped establish its position as a sovereign state and confronted it with both the opportunities and the dilemmas associated with problems of international co-operation and attempts to prevent war.