24 Oct 1945, after World War II: UN established. New Year's Day 1942: US, UK, USSR and China signed United Nations Declaration

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The United Nations (UN) is an intergovernmental organization to promote international co-operation, established on 24 October 1945 after World War II in order to prevent another such conflict. At its founding, the UN had 51 member states; there are now 193.
The headquarters of the United Nations is in Manhattan, New York City, and experiences extraterritoriality. Further main offices are situated in Geneva, Nairobi and Vienna.
- UN Charter signed 26 June 1945
- Charter entered into force 24 October 1945
There are six official languages of the UN.
These are Arabic, Chinese, English, French, Russian and Spanish.

1942 "Declaration of United Nations" by the Allies of World War II
The earliest concrete plan for a new world organization began under the aegis of the US State Department in 1939. The text of the "Declaration by United Nations" was drafted by President Franklin Roosevelt, British Prime Minister Winston Churchill, and Roosevelt aide Harry Hopkins, while meeting at the White House, 29 December 1941. It incorporated Soviet suggestions, but left no role for France. "Four Policemen" was coined to refer four major Allied countries, United States, United Kingdom, Soviet Union, and China, which was emerged in Declaration by United Nations. Roosevelt first coined the term United Nations to describe the Allied countries."On New Year's Day 1942, President Roosevelt, Prime Minister Churchill, Maxim Litvinov, of the USSR, and T. V. Soong, of China, signed a short document which later came to be known as the United Nations Declaration and the next day the representatives of twenty-two other nations added their signatures."

A JOINT DECLARATION BY THE UNITED STATES OF AMERICA, THE UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND, THE UNION OF SOVIET SOCIALIST REPUBLICS, CHINA, AUSTRALIA, BELGIUM, CANADA, COSTA RICA, CUBA, CZECHOSLOVAKIA, DOMINICAN REPUBLIC, EL SALVADOR, GREECE, GUATEMALA, HAITI, HONDURAS, INDIA, LUXEMBOURG, NETHERLANDS, NEW ZEALAND, NICARAGUA, NORWAY, PANAMA, POLAND, SOUTH AFRICA, YUGOSLAVIA
The Governments signatory hereto,
Having subscribed to a common program of purposes and principles embodied in the Joint Declaration of the President of the United States of America and the Prime Minister of Great Britain dated August 14, 1941, known as the Atlantic Charter,
Being convinced that complete victory over their enemies is essential to defend life, liberty, independence and religious freedom, and to preserve human rights and justice in their own lands as well as in other lands, and that they are now engaged in a common struggle against savage and brutal forces seeking to subjugate the world,
DECLARE:
(1) Each Government pledges itself to employ its full resources, military or economic, against those members of the Tripartite Pact and its adherents with which such government is at war.
(2) Each Government pledges itself to cooperate with the Governments signatory hereto and not to make a separate armistice or peace with the enemies.
The foregoing declaration may be adhered to by other nations which are, or which may be, rendering material assistance and contributions in the struggle for victory over Hitlerism.

The Charter of the United Nations is the foundational treaty of the intergovernmental organization; the United Nations. It was signed at the San Francisco War Memorial and Performing Arts Center in San Francisco, United States, on 26 June 1945, by 50 of the 51 original member countries. (Poland, the other original member, which was not represented at the conference, signed it two months later.) It entered into force on 24 October 1945, after being ratified by the original five permanent members of the Security Council—the Republic of China (later replaced by the People's Republic of China), France, the Union of Soviet Socialist Republics (later replaced by the Russian Federation), the United Kingdom, and the United States—and a majority of the other signatories.

The headquarters of the United Nations is in Manhattan, New York City, and experiences extraterritoriality. Further main offices are situated in Geneva, Nairobi and Vienna. The organization is financed by assessed and voluntary contributions from its member states. Its objectives include maintaining international peace and security, promoting human rights, fostering social and economic development, protecting the environment, and providing humanitarian aid in cases of famine, natural disaster, and armed conflict.

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