Founding of the League of Nations
Also called: League of Nations
Proposed by Wilson, the first international organization to keep world peace was set up in Geneva, Switzerland. But the United States stayed out and the League had no military means of enforcement, so it failed to stop aggression.

RomanDeckert · CC BY-SA 4.0 · Source
The League of Nations came into being on 10 January 1920, when its Covenant — the first part of the Treaty of Versailles — took effect. With its headquarters in Geneva, it had an Assembly of all members, a Council with Britain, France, Italy and Japan as permanent members, and a Secretariat, alongside the International Labour Organization and the Permanent Court of International Justice. Some forty countries attended its first Assembly in November.
The League mediated disputes, worked on disarmament, refugee relief and public health, and supervised the former colonies of the defeated powers as mandates. But the United States never joined because of Senate opposition, and Germany (1926) and the Soviet Union (1934) came in late. Decisions required unanimity, and lacking an army to confront aggressors, the League relied on economic sanctions.
It failed to stop Japan’s seizure of Manchuria and Italy’s invasion of Ethiopia in the 1930s, and lost authority as Japan, Germany and Italy walked out. Having failed to prevent the Second World War, the League was dissolved in 1946, and its experience fed into the creation of the United Nations.