United Nations (UN), international organization established on October 24, 1945. The United Nations (UN) was the second multipurpose international organization established in the 20th century that was worldwide in scope and membership. Its predecessor, the League of Nations, was created by the Treaty of Versailles in 1919 and disbanded in 1946. Headquartered in New York City, the UN also has regional offices in Geneva, Vienna, and Nairobi. Its official languages are Arabic, Chinese, English, French, Russian, and Spanish. For a list of UN member countries and secretaries-general, see below.

(Read Ted Turner’s Britannica entry on the U.N. Foundation.)

According to its Charter, the UN aims:

to save succeeding generations from the scourge of war,…to reaffirm faith in fundamental human rights,…to establish conditions under which justice and respect for the obligations arising from treaties and other sources of international law can be maintained, and to promote social progress and better standards of life in larger freedom.

In addition to maintaining peace and security, other important objectives include developing friendly relations among countries based on respect for the principles of equal rights and self-determination of peoples; achieving worldwide cooperation to solve international economic, social, cultural, and humanitarian problems; respecting and promoting human rights; and serving as a centre where countries can coordinate their actions and activities toward these various ends.

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The UN formed a continuum with the League of Nations in general purpose, structure, and functions; many of the UN’s principal organs and related agencies were adopted from similar structures established earlier in the century. In some respects, however, the UN constituted a very different organization, especially with regard to its objective of maintaining international peace and security and its commitment to economic and social development.

Changes in the nature of international relations resulted in modifications in the responsibilities of the UN and its decision-making apparatus. Cold War tensions between the United States and the Soviet Union deeply affected the UN’s security functions during its first 45 years. Extensive post-World War II decolonization in Africa, Asia, and the Middle East increased the volume and nature of political, economic, and social issues that confronted the organization. The Cold War’s end in 1991 brought renewed attention and appeals to the UN. Amid an increasingly volatile geopolitical climate, there were new challenges to established practices and functions, especially in the areas of conflict resolution and humanitarian assistance. At the beginning of the 21st century, the UN and its programs and affiliated agencies struggled to address humanitarian crises and civil wars, unprecedented refugee flows, the devastation caused by the spread of AIDS, global financial disruptions, international terrorism, and the disparities in wealth between the world’s richest and poorest peoples.

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History and development

Despite the problems encountered by the League of Nations in arbitrating conflict and ensuring international peace and security prior to World War II, the major Allied powers agreed during the war to establish a new global organization to help manage international affairs. This agreement was first articulated when U.S. President Franklin D. Roosevelt and British Prime Minister Winston Churchill signed the Atlantic Charter in August 1941. The name United Nations was originally used to denote the countries allied against Germany, Italy, and Japan. On January 1, 1942, 26 countries signed the Declaration by United Nations, which set forth the war aims of the Allied powers.

The United States, the United Kingdom, and the Soviet Union took the lead in designing the new organization and determining its decision-making structure and functions. Initially, the “Big Three” states and their respective leaders (Roosevelt, Churchill, and Soviet premier Joseph Stalin) were hindered by disagreements on issues that foreshadowed the Cold War. The Soviet Union demanded individual membership and voting rights for its constituent republics, and Britain wanted assurances that its colonies would not be placed under UN control. There also was disagreement over the voting system to be adopted in the Security Council, an issue that became famous as the “veto problem.”

The first major step toward the formation of the United Nations was taken August 21–October 7, 1944, at the Dumbarton Oaks Conference, a meeting of the diplomatic experts of the Big Three powers plus China (a group often designated the “Big Four”) held at Dumbarton Oaks, an estate in Washington, D.C. Although the four countries agreed on the general purpose, structure, and function of a new world organization, the conference ended amid continuing disagreement over membership and voting. At the Yalta Conference, a meeting of the Big Three in a Crimean resort city in February 1945, Roosevelt, Churchill, and Stalin laid the basis for charter provisions delimiting the authority of the Security Council. Moreover, they reached a tentative accord on the number of Soviet republics to be granted independent memberships in the UN. Finally, the three leaders agreed that the new organization would include a trusteeship system to succeed the League of Nations mandate system.

The Dumbarton Oaks proposals, with modifications from the Yalta Conference, formed the basis of negotiations at the United Nations Conference on International Organization (UNCIO), which convened in San Francisco on April 25, 1945, and produced the final Charter of the United Nations. The San Francisco conference was attended by representatives of 50 countries from all geographic areas of the world: 9 from Europe, 21 from the Americas, 7 from the Middle East, 2 from East Asia, and 3 from Africa, as well as 1 each from the Ukrainian Soviet Socialist Republic and the Belorussian Soviet Socialist Republic (in addition to the Soviet Union itself) and 5 from British Commonwealth countries. Poland, which was not present at the conference, was permitted to become an original member of the UN. Security Council veto power (among the permanent members) was affirmed, though any member of the General Assembly was able to raise issues for discussion. Other political issues resolved by compromise were the role of the organization in the promotion of economic and social welfare; the status of colonial areas and the distribution of trusteeships; the status of regional and defense arrangements; and Great Power dominance versus the equality of states. The UN Charter was unanimously adopted and signed on June 26 and promulgated on October 24, 1945.