The diplomatic philosophy behind the League represented a fundamental shift from the preceding hundred years. The League lacked its own armed force and depended on the victorious Great Powers of World War I (France, the UK, Italy and Japan were the permanent members of the executive Council) to enforce its resolutions, keep to its economic sanctions, or provide an army when needed. The Great Powers were often reluctant to do so. Sanctions could hurt League members, so they were reluctant to comply with them. During the Second Italo-Abyssinian War, when the League accused Italian soldiers of targeting Red Cross medical tents, Benito Mussolini responded that "the League is very well when sparrows shout, but no good at all when eagles fall out."
After some notable successes and some early failures in the 1920s, the League ultimately proved incapable of preventing aggression by the Axis powers in the 1930s. The credibility of the organization was weakened by the fact that the United States never officially joined the League and the Soviet Union joined late and only briefly. Germany withdrew from the League, as did Japan, Italy, Spain and others. The onset of the Second World War showed that the League had failed its primary purpose, which was to prevent any future world war. The League lasted for 26 years; the United Nations (UN) replaced it after the end of the Second World War and inherited several agencies and organisations founded by the League.
The concept of a peaceful community of nations had been proposed as far back 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. Kant argued for the establishment of a peaceful world community, not in a sense of a global government, but in the hope that each state would declare itself a free state that respects its citizens and welcomes foreign visitors as fellow rational beings, thus promoting peaceful society worldwide. International co-operation to promote collective security originated in the Concert of Europe that developed after the Napoleonic Wars in the 19th century in an attempt to maintain the status quo between European states and so avoid war. This period also saw the development of international law, with the first Geneva Conventions establishing laws dealing with humanitarian relief during wartime, and the international Hague Conventions of 1899 and 1907 governing rules of war and the peaceful settlement of international disputes. As historians William H. Harbaugh and Ronald E. Powaski point out, Theodore Roosevelt was the first American President to call for an international league. At the acceptance for his Nobel Prize, Roosevelt said: "it would be a masterstroke if those great powers honestly bent on peace would form a League of Peace."
The forerunner of the League of Nations, the Inter-Parliamentary Union (IPU), was formed by the peace activists William Randal Cremer and Frédéric Passy in 1889 (and is currently still in existence as an international body with a focus on the various elected legislative bodies of the world.) The IPU was founded with an international scope, with a third of the members of parliaments (in the 24 countries that had parliaments) serving as members of the IPU by 1914. Its foundational aims were to encourage governments to solve international disputes by peaceful means. Annual conferences were established to help governments refine the process of international arbitration. Its structure was designed as a council headed by a president, which would later be reflected in the structure of the League.
At the start of the First World War the first schemes for international organisation to prevent future wars began to gain considerable public support, particularly in Great Britain and the United States. Goldsworthy Lowes Dickinson, a British political scientist, coined the term "League of Nations" in 1914 and drafted a scheme for its organisation. Together with Lord Bryce, he played a leading role in the founding of the group of internationalist pacifists known as the Bryce Group, later the League of Nations Union. The group became steadily more influential among the public and as a pressure group within the then governing Liberal Party. In Dickinson's 1915 pamphlet After the War he wrote of his "League of Peace" as being essentially an organisation for arbitration and conciliation. He felt that the secret diplomacy of the early twentieth century had brought about war and thus could write that, "the impossibility of war, I believe, would be increased in proportion as the issues of foreign policy should be known to and controlled by public opinion." The ‘Proposals’ of the Bryce Group were circulated widely, both in England and the US, where they had a profound influence on the nascent international movement.