What's the UN?
From Grolier's The New Book of Knowledge

The United Nations is a voluntary association of nations. Organized in 1945 at the end of World War II (1939–45), it was designed to keep peace in the world, to promote people's general welfare, and to support the liberties and rights of individuals to determine their own future.

The United Nations is divided into several organs, or branches. These organs function somewhat similarly to those of the legislative, executive, and judicial branches of national governments. However, the United Nations does not have as much power over its member nations as national governments have over their citizens. Its success depends on the willingness of the member nations to cooperate in good faith.

The idea of having an international organization to keep the peace and provide for the general welfare did not start with the United Nations. After World War I (1914–18), Woodrow Wilson, who was then President of the United States, came up with the idea for the League of Nations, which was incorporated into the 1919 peace treaty. However, the U.S. Senate refused to ratify the treaty and therefore did not join the League of Nations. Nevertheless, the League of Nations became an active organization and in some ways was effective—until World War II began in 1939.

Leland Goodrich
Author, The United Nations