The League of Nations was the direct product of the fourteenth and final point in US President Woodrow Wilson's January 1918 'Fourteen Points' address. The First World War had brought down four empires and killed tens of millions; Wilson's hope was that, to prevent such a war from recurring, states would consent to partially limit their sovereignty under the collective-security umbrella of a 'league of nations.' The League's Covenant was written as the first 26 articles of the Treaty of Versailles, signed on 28 June 1919, and entered into force on 10 January 1920.

The organisation's core logic was that if one state attacked another, the remaining members would collectively impose economic and, if necessary, military sanctions (Article 16). A General Assembly meeting in Geneva, together with a Council composed of four permanent members (Britain, France, Italy, Japan) and four rotating ones, formed the decision-making organs. A Permanent Court of International Justice (the ancestor of today's ICJ) and the International Labour Organization were established alongside — and the ILO survives to this day. Yet structural weaknesses were visible from the start: the US Senate, treating collective-security obligations as a threat to sovereignty, rejected both Versailles and League membership; the Bolshevik Soviet Union was excluded for years; defeated Germany was not admitted until 1926.

The 1920s brought modest successes — the Åland Islands dispute, the arbitration over Upper Silesia, administration of the Saar. The real test came in the 1930s, and the League failed in succession: the 1931 Japanese invasion of Manchuria (the Lytton Report blamed Japan; Japan withdrew in 1933), the 1935 Italian assault on Ethiopia (sanctions were diluted and never extended to oil), the 1936 remilitarisation of the Rhineland, the 1937 Spanish Civil War, the 1939 Soviet invasion of Finland. Germany and Japan withdrew in 1933, Italy in 1937. The structural cause of the collapse was not merely missing members but the absence of political will and concrete military force to back collective security — the great powers refused to act together whenever their own interests were squeezed.

Even so, reading the League as nothing but a failure misreads the history. It proved that states could conduct standing diplomatic negotiation under a permanent roof, and the United Nations, founded in 1945, was deliberately designed by learning from the League's failures (granting the Security Council enforcement powers, keeping the United States at the centre, building a worldwide office network). The ILO, the cultural-cooperation office that preceded UNESCO, the International Court of Justice, the High Commissioner for Refugees — all the foundations of today's multilateral system were rehearsed in Geneva. The first encounter between idealism and reality left behind not a legacy but a toolkit.