1943 sketch by Franklin Roosevelt of the UN original three branches: The
, an executive branch, and an international assembly of forty UN member states.
In the century prior to the UN's creation, several international treaty organizations and conferences had been formed to regulate conflicts between nations, such as the
International Committee of the Red Cross and the
Hague Conventions of 1899 and 1907. Following the catastrophic loss of life in the
First World War, the
Paris Peace Conference established the
League of Nations to maintain harmony between countries. This organization resolved some territorial disputes and created international structures for areas such as postal mail, aviation, and opium control, some of which would later be absorbed into the UN. However, the League lacked representation for colonial peoples (then half the world's population) and significant participation from several major powers, including the US, USSR, Germany, and Japan; it failed to act against the
Japanese invasion of Manchuria in 1931, the
Second Italo-Ethiopian War in 1935, the
Japanese invasion of China in 1937, and German expansions under
Adolf Hitler that culminated in the
Second World War.
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 to four major Allied countries,
Soviet Union, and
China, which emerged in the Declaration by United Nations.
 Roosevelt first coined the term United Nations to describe the
[b] "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."
 The term United Nations was first officially used when 26 governments signed this Declaration. One major change from the
Atlantic Charter was the addition of a provision for religious freedom, which Stalin approved after Roosevelt insisted.
 By 1 March 1945, 21 additional states had signed.
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,
- 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.
- 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.
During the war, "the United Nations" became the official term for the
Allies. To join, countries had to sign the Declaration and declare war on the
The UN in 1945. In light blue, the founding members. In dark blue, protectorates and territories of the founding members.
The UN was formulated and negotiated among the delegations from
the Allied Big Four (the
Soviet Union, the
China) at the
Dumbarton Oaks Conference in 1944.
 After months of planning, the
UN Conference on International Organization opened in
San Francisco, 25 April 1945, attended by 50 governments and a number of non-governmental organizations involved in drafting the
"The heads of the delegations of the sponsoring countries took turns as chairman of the plenary meetings:
Anthony Eden, of Britain,
Edward Stettinius, of the United States,
T. V. Soong, of China, and
Vyacheslav Molotov, of the Soviet Union. At the later meetings,
Lord Halifax deputized for Mr. Eden,
Wellington Koo for T. V. Soong, and Mr
Gromyko for Mr. Molotov."
 The UN officially came into existence 24 October 1945, upon ratification of the Charter by the five permanent members of the Security Council—France, the
Republic of China, the Soviet Union, the UK and the US—and by a majority of the other 46 signatories.
The first meetings of the General Assembly, with 51 nations represented,
[c] and the Security Council took place in
London beginning 10 January 1946.
 The General Assembly selected New York City as the site for the headquarters of the UN, and the facility was completed in 1952. Its site—like UN headquarters buildings in
Nairobi—is designated as
 The Norwegian Foreign Minister,
Trygve Lie, was elected as the first UN Secretary-General.
Cold War era
was a particularly active Secretary-General from 1953 until his death in 1961.
Though the UN's primary mandate was
peacekeeping, the division between the US and USSR often paralysed the organization, generally allowing it to intervene only in conflicts distant from the
Cold War. (A notable exception was a Security Council resolution in 1950 authorizing a US-led coalition to repel the
North Korean invasion of South Korea, passed in the absence of the USSR.)
 In 1947, the General Assembly approved
a resolution to partition Palestine, approving the creation of the state of
Israel. Two years later,
Ralph Bunche, a UN official, negotiated an armistice to the resulting conflict. In 1956, the
first UN peacekeeping force was established to end the
 however, the UN was unable to intervene against the USSR's simultaneous invasion of Hungary following
that country's revolution.
In 1960, the UN deployed
United Nations Operation in the Congo (UNOC), the largest military force of its early decades, to bring order to the breakaway
State of Katanga, restoring it to the control of the
Democratic Republic of the Congo by 1964. While travelling to meet with rebel leader
Moise Tshombe during the conflict,
Dag Hammarskjöld, often named as one of the UN's most effective Secretaries-General,
died in a plane crash; months later he was posthumously awarded the
Nobel Peace Prize. In 1964, Hammarskjöld's successor,
U Thant, deployed the
UN Peacekeeping Force in Cyprus, which would become one of the UN's longest-running peacekeeping missions.
With the spread of
decolonization in the 1960s, the organization's membership saw an influx of newly independent nations. In 1960 alone, 17 new states joined the UN, 16 of them from Africa.
 On 25 October 1971, with opposition from the United States, but with the support of many
Third World nations, the mainland, communist
People's Republic of China was given the Chinese seat on the Security Council in place of the
Republic of China that occupied Taiwan; the vote was widely seen as a sign of waning US influence in the organization. Third World nations organized into the
Group of 77 coalition under the leadership of Algeria, which briefly became a dominant power at the UN. In 1975, a bloc comprising the USSR and Third World nations passed
a resolution, over strenuous US and Israeli opposition, declaring
Zionism to be racism; the resolution was repealed in 1991, shortly after the end of the Cold War.
With an increasing Third World presence and the failure of UN mediation in conflicts in the
Kashmir, the UN increasingly shifted its attention to its ostensibly secondary goals of economic development and cultural exchange. By the 1970s, the UN budget for social and economic development was far greater than its peacekeeping budget.
After the Cold War, the UN saw a radical expansion in its peacekeeping duties, taking on more missions in ten years than it had in the previous four decades. Between 1988 and 2000, the number of adopted Security Council resolutions more than doubled, and the peacekeeping budget increased more than tenfold.
 The UN negotiated an end to the
Salvadoran Civil War, launched a successful
peacekeeping mission in Namibia, and oversaw democratic elections in post-
apartheid South Africa and post-
Khmer Rouge Cambodia.
 In 1991, the UN authorized a
US-led coalition that repulsed the Iraqi
invasion of Kuwait.
Brian Urquhart, Under-Secretary-General from 1971 to 1985, later described the hopes raised by these successes as a "false renaissance" for the organization, given the more troubled missions that followed.
Though the UN Charter had been written primarily to prevent aggression by one nation against another, in the early 1990s the UN faced a number of simultaneous, serious crises within nations such as Somalia, Haiti, Mozambique, and the former Yugoslavia. The
UN mission in Somalia was widely viewed as a failure after the US withdrawal following casualties in the
Battle of Mogadishu, and the
UN mission to Bosnia faced "worldwide ridicule" for its indecisive and confused mission in the face of ethnic cleansing.
 In 1994, the
UN Assistance Mission for Rwanda failed to intervene in the
Rwandan genocide amid indecision in the Security Council.
Beginning in the last decades of the Cold War, American and European critics of the UN condemned the organization for perceived mismanagement and corruption. In 1984, the US President,
Ronald Reagan, withdrew his nation's funding from
UNESCO (the United Nations Educational, Scientific and Cultural Organization, founded 1946) over allegations of mismanagement, followed by Britain and Singapore.
Boutros Boutros-Ghali, Secretary-General from 1992 to 1996, initiated a reform of the Secretariat, reducing the size of the organization somewhat.
 His successor,
Kofi Annan (1997–2006), initiated further management reforms in the face of threats from the United States to withhold its UN dues.
In the late 1990s and 2000s, international interventions authorized by the UN took a wider variety of forms. The
UN mission in the
Sierra Leone Civil War of 1991–2002 was supplemented by British
Royal Marines, and the
invasion of Afghanistan in 2001 was overseen by
NATO.In 2003, the United States
invaded Iraq despite failing to pass a UN Security Council resolution for authorization, prompting a new round of questioning of the organization's effectiveness. Under the eighth Secretary-General,
Ban Ki-moon, the UN has intervened with peacekeepers in crises including the
War in Darfur in Sudan and the
Kivu conflict in the Democratic Republic of Congo and sent observers and chemical weapons inspectors to the
Syrian Civil War.
 In 2013,
an internal review of UN actions in
the final battles of the
Sri Lankan Civil War in 2009 concluded that the organization had suffered "systemic failure".
 One hundred and one UN personnel died in the
2010 Haiti earthquake, the worst loss of life in the organization's history.
Millennium Summit was held in 2000 to discuss the UN's role in the 21st century.
 The three day meeting was the largest gathering of world leaders in history, and culminated in the adoption by all member states of the
Millennium Development Goals (MDGs), a commitment to achieve international development in areas such as
gender equality, and
public health. Progress towards these goals, which were to be met by 2015, was ultimately uneven. The
2005 World Summit reaffirmed the UN's focus on promoting development, peacekeeping, human rights, and global security.
Sustainable Development Goals were launched in 2015 to succeed the Millennium Development Goals.
In addition to addressing global challenges, the UN has sought to improve its accountability and democratic legitimacy by engaging more with civil society and fostering a global constituency.
 In an effort to enhance transparency, in 2016 the organization held its first public debate between candidates for Secretary-General.
 On January 1, 2017, Portuguese diplomat
António Guterres, who previously served as
UN High Commissioner for Refugees, became the ninth Secretary-General. Guterres has highlighted several key goals for his administration, including an emphasis on diplomacy for preventing conflicts, more effective peacekeeping efforts, and streamlining the organization to be more responsive and versatile to global needs.