Where and when did the preparation for the founding of the United Nations begin?

Shortly before the end of World War Ⅱ, leaders of many nations, including the United States, decided to form an international organization. It was hoped that nations could discuss their disagreements in this organization instead of fighting over them.
    On April 25, 1945, two hundred representatives from many nations came to San Francisco, California, to make the rules that would govern this organization. After many months of hard work, arguments, and compromises, the United Nations organization was founded. Today thousands of people visit the United Nations headquarters in New York City. They see the large rooms where representatives from about a hundred nations meet to discuss their problems. They find out about the work of the United Nations. Children who visit the United Nations are especially interested in learning about the help given to children. Teams of workers from the United Nations visit countries in Latin America, Africa and Asia to help children who are sick and hungry. They bring food and medicine. They also teach people what doctors have learned about keeping children strong. People who work for the United Nations believe that happy, healthy people are more likely to be friendly to other nations. They believe that helping people will help the world be at peace.