The League of Nations, a former international organization, was formed after World War I to promote international peace and security. The basis of the League, also called the Covenant, was written into the Treaty of Versailles and other peace treaties and provided for an assembly, a council, and a secretariat. Because the peace treaties had created the League of Nations, the League was bound to uphold their principles. but however, it became apparent that some of the terms of the treaties were harsh and unjust and needed amending. This undermined the league. Woodrow Wilson hoped however, by including it in the treaties that this would ensure that the League was accepted by all nations. However, from the start, the League shared many of the weaknesses of the treaties themselves. The defeated powers were not consulted about the league and were not invited to join. The victorious powers did not really agree among themselves about the League.

A system of colonial commands was also set up. Based in Geneva, the League proved useful in settling minor international disputes, but they had a hard time stopping aggression involving major powers such as, Japan's occupation of Manchuria in 1931, Italy's invasion of Ethiopia in 1935-36, and Germany's seizure of Austria in 1938. It collapsed early in World War II and ended in 1946.

Its ending in 1946 was because it had some basic and fundamental problems such as dealing with aggression involving major powers. Countries like Japan and Italy were able to just walk over the League of Nations because it had no armed forces of its own and it relied upon the co-operation of its members. This problem was inter-linked with the fact that the League was very slow at making decisions. With no armed forces this made it difficult to impose decisions. Therefore when a crisis occurred the league was supposed to act fast with resoluteness. Although, often the League met too infrequently and took far too long to make critical decisions. This need for all members to agree on a course of action undermined the strength of the League. The League was too indecisive they needed some influential countries. The absence of the powerful USA and, until 1934, the USSR were felt, this could have been the answer to the League's problems. However these countries did not join and again this contributed the failure of the league, as non-members, they could and did trade with countries facing League sanctions and therefore to a certain extent it was in their own interests to remain detached from such a commitment as the League. Another problem for the League however, was that it was being too closely linked to the victors of the First World War and the Peace Treaties.

Another reason why the league failed was that because one their aims, 'To keep collective security…' failed. Britain and France along with other members were more concerned about their own interests. As a result they were reluctant to get involved in collective security (one of the reasons why Britain and France were reluctant to commit troops to fight for the League of Nations) and their League could not make powerful countries obey their rulings.

The League also failed because there was a lack of unity between Britain and France. They often disagreed and they did not trust each other. With this and the fact decisions had to be unanimous made it almost impossible for the League to make a decision.

The League was also weakened by the Great Depression that hit the world in the years following the Wall Street Crash. At a time of economic crises it meant that the League had trouble imposing sanctions especially at this time. This meant that countries like Japan and Italy were able to annex other countries without effective punishment.

All these reasons did not fear the likes of Hitler and Mussolini; in fact they gained in confidence. Therefore the failure of the League was really a vicious circle as the basic problems led to other problems and encouraged the rise of powerful nationalist dictators and militaristic governments prepared to ignore the League and to use force.