The main purpose for the formation of both the League of Nations and the United Nations was to

League of Nations, an organization for international cooperation established on January 10, 1920, at the initiative of the victorious Allied powers at the end of World War I. The central, basic idea of the movement was that aggressive war is a crime not only against the immediate victim but against the whole human community. Accordingly it is the right and duty of all states to join in preventing it; if it is certain that they will so act, no aggression is likely to take place. Such affirmations might be found in the writings of philosophers or moralists but had never before emerged onto the plane of practical politics. Statesmen and lawyers alike held and acted on the view that there was no natural or supreme law by which the rights of sovereign states, including that of making war as and when they chose, could be judged or limited. Many of the attributes of the League of Nations were developed from existing institutions or from time-honoured proposals for the reform of previous diplomatic methods. However, the premise of collective security was, for practical purposes, a new concept engendered by the unprecedented pressures of World War I.

Explanation:

The central, basic idea of the movement was that aggressive war is a crime not only against the immediate victim but against the whole human community. Accordingly it is the right and duty of all states to join in preventing it; if it is certain that they will so act, no aggression is likely to take place. Such affirmations might be found in the writings of philosophers or moralists but had never before emerged onto the plane of practical politics. Statesmen and lawyers alike held and acted on the view that there was no natural or supreme law by which the rights of sovereign states, including that of making war as and when they chose, could be judged or limited. Many of the attributes of the League of Nations were developed from existing institutions or from time-honoured proposals for the reform of previous diplomatic methods. However, the premise of collective security was, for practical purposes, a new concept engendered by the unprecedented pressures of World War I.