The creation of the UN at the San Francisco Conference in June 1945 was the culmination of four years of concentrated preparation. During these years, the idea of a world organization to replace the League of Nations was first debated and then fleshed out. Many of the important principles of the UN adopted at San Francisco were derived from earlier conferences.
The new world body officially came into being on 24 October 1945, when the Charter had been duly ratified by all permanent members of the Security Council and a majority of the other original signatory powers. This date is universally celebrated as United Nations Day.