The concept of a peaceful community of nations had been proposed as early as 1795, when Immanuel Kant's Perpetual Peace: A Philosophical Sketch outlined the idea of a league of nations to control conflict and promote peace between states.

In January 1915, a peace conference directed by Jane Addams was held in the neutral United States. The delegates adopted a platform calling for creation of international bodies with administrative and legislative powers to develop a "permanent league of neutral nations" to work for peace and disarmament.

In 1915, a similar body to the Bryce group was set up in the United States led by former president William Howard Taft. It was called the League to Enforce Peace.

The conferees came out of the Paris Peace Conference and agreed to maintain permanent peace after World War I, and agreed to form the League of Nations called for by President Wilson on January 25, 1919.

On 28 June 1919, 44 states signed the Covenant, including 31 states which had taken part in the war on the side of the Triple Entente or joined it during the conflict.

The League of Nations held its first meeting on January 16, 1920, that is, six days after the entry into force of the Treaty of Versailles and the official end of World War I.

Poland and Lithuania both regained their independence but soon became immersed in territorial disputes. During the Polish–Soviet War, Lithuania signed the Moscow Peace Treaty with the Soviet Union that laid out Lithuania's frontiers. On 7 October 1920, the League negotiated the Suwałki Agreement establishing a cease-fire and a demarcation line between the two nations.

In June 1921, the League announced its decision: the islands were to remain a part of Finland, but with guaranteed protection of the islanders, including demilitarisation. With Sweden's reluctant agreement, this became the first European international agreement concluded directly through the League.

In November 1921, the League decided that the frontiers of Albania should be the same as they had been in 1913, with three minor changes that favoured Yugoslavia. Yugoslav forces withdrew a few weeks later, albeit under protest.

The Salomón–Lozano Treaty was signed in July 1922 by representatives Fabio Lozano Torrijos, of Colombia and Alberto Salomón Osorio of Peru. The fourth in a succession of treaties on the Colombian-Peruvian disputes over land in the upper Amazon region, it was intended to be a comprehensive settlement of the long border dispute between the two countries.

The Klaipėda Revolt took place in January 1923 in the Klaipėda Region . The region, located north of the Neman River, was detached from East Prussia, German Empire by the Treaty of Versailles and became a mandate of the League of Nations.

Incident at Petrich was a Greek–Bulgarian crisis in 1925 that resulted in a brief invasion of Bulgaria by Greece near the border town of Petrich after the killing of a Greek captain and a sentry by Bulgarian soldiers. The incident ended after a decision by the League of Nations.

The League resolved a dispute between the kingdom of Iraq and the Republic of Turkey over control of the former Ottoman province of Mosul in 1926.

The Lytton Report appeared a year later (October 1932). It declared Japan to be the aggressor and demanded Manchuria be returned to China. The report passed 42–1 in the Assembly in 1933 (only Japan voting against), but instead of removing its troops from China, Japan withdrew from the League. In the end, as British historian Charles Mowat argued, collective security was dead.

A referendum on territorial status was held in the Territory of the Saar Basin on 13 January 1935. Over 90% of voters opted for reunification with Germany, with 9% voting for the status quo as a League of Nations mandate territory and less than 0.5% opting for unification with France.

The Sanjak of Alexandretta in the French Mandate of Syria was given autonomy in 1937.

On 26 May 1937, Egypt became the last state to join the League.

Between 1920 and 1939, a total of 63 countries became member states of the League of Nations. The Covenant forming the League of Nations was included in the Treaty of Versailles and came into force on 10 January 1920, with the League of Nations being dissolved on 18 April 1946; its assets and responsibilities were transferred to the United Nations.

First Soviet-Finnish War, was a war between the Soviet Union and Finland. The war began with a Soviet invasion of Finland on 30 November 1939, three months after the outbreak of World War II, and ended three-and-a-half months later with the Moscow Peace Treaty on 13 March 1940.