How did the failure of the league of nations give rise to the United Nations?

Actually, UN is the successor of League of Nations. After the end of the league, i.e, after the outbreak of second world war, the members thought it was better to form a new world organization rather than reforming the League.That's how UN was created, and the UN wouldn't have existed if the league had. so there's no question of UN playing ANY role in the end of the League of Nations..!!!