(1) In spite of the fact that the League of Nations had failed to establish world peace, the leaders of major countries were aware of the need to have another international organisation to preserve World Peace.
(2) The destruction caused by the Second World War was enormous.
(3) The dropping of atom bombs on Japan and the destruction caused by it made the World leaders to establish the United Nations to prevent an all-destructive nuclear Third World War.
Therefore, after the end of the Second World War, the United Nations was established.