The Allies met in several conferences from 1941 to 1945 to discuss how to guarantee a more peaceful and cooperative world once the Second World War (1939 to 45) was concluded. To foster global cooperation, facilitate free trade, and give aid to war-ravaged and developing countries, the United Nations was formed along with other new international bodies such as the International Monetary Fund, World Bank, and International Court of Justice. This terrible global conflict had, it was hoped, at least led to a solution for lasting peace.

The first truly global political body was the League of Nations, born from the Treaty of Versailles, which had formally concluded the First World War (1914 to 18). In a project driven by the US President Woodrow Wilson (1856 to 1924), the League was founded in January 1920 to promote world peace and welfare. It provided a forum, at its headquarters in Geneva, where 44 countries promised to resolve international disputes peacefully. Any state that attacked another would be subjected to the collective action of all the other members, first in the form of economic sanctions, and if necessary, military action. This idea was known as 'collective security.' Other aims included the fostering of international cooperation in economics and social matters, particularly in the fields of health and communications.

Unfortunately, the League of Nations suffered from several inherent weaknesses. Perhaps the most significant was the absence of the United States, a decision taken because isolationists dominated post-war US politics. The League also failed to respond adequately to several direct challenges, notably Japan's occupation of Manchuria in China in 1931 and Italy's invasion of Abyssinia (modern Ethiopia) in 1935. The consequence of the League's weaknesses was that individual members began to concentrate not on collective security but on making their own treaties and the use of military force to achieve foreign policy objectives. By 1939, the League had been marginalised regarding world affairs, but the essential idea would be revived, even while the world was fully occupied with the largest conflict ever experienced.

The commonly held view amongst the Allies (notably the US, Britain, France, and the USSR) during WWII was that free trade and the absence of tariffs, and economic and political stability made peace much more likely than war between states. Countries had not cooperated in matters of finance and economics during the 1930s, and it was widely felt that this was one of the causes of WWII.

President Franklin D. Roosevelt (1882 to 1945) had long been a supporter of the idea that the League of Nations have a successor international organisation which could promote world peace once WWII was concluded. This organisation would be called the United Nations (UN). Roosevelt had already made some gains in this direction when he signed the Atlantic Charter with British Prime Minister Winston Churchill (1874 to 1965) on 14 August 1941. This charter set out that all peoples – victors or losers in the war – "were entitled to self determination and a fair share of the world's resources" (Boatner, 647), that is, access to natural resources and trade networks.

Next came the United Nations Declaration of 1 January 1942, made jointly by Roosevelt and Churchill. The declaration included the first official use of the term 'United Nations' to refer to an international organisation of cooperation. The declaration was signed by the US, UK, USSR, and China, as well as 22 other states at a later date. This was followed up by the Four-Power Declaration signed in Moscow on 30 October 1943, again by the US, UK, USSR, and China, which repeated the promise that an international organisation of peace and cooperation would be created once the war was over. This sentiment was reinforced at the Tehran Conference of November-December 1943, where Roosevelt, Stalin, and Churchill all met.

The Bretton Woods Conference was held at Bretton Woods in the US state of New Hampshire, running from 1 to 22 July 1944. The meeting is also known as the United Nations Monetary and Financial Conference. The decisions taken by the delegates from 44 states were long-lasting. The two men most responsible for the meeting were John Maynard Keynes (1883 to 1946), the British economist and government adviser, and Harry Dexter White (1892 to 1948), then US treasury assistant.

At Bretton Woods, the idea of the UN took another significant step closer to becoming a reality when it was decided to create the International Monetary Fund (IMF). The IMF began operations in December 1945 and had 22 participating countries. The IMF was designed to act like a central bank and help certain states redress imbalances of international payments, which it was hoped would stabilise international exchange rates and prevent the use of trade barriers such as tariffs.

Alongside the IMF, the Bretton Woods delegates also created the International Bank for Reconstruction and Development (IBRD), which would later become known simply as the World Bank. The IBRD was given $10 billion as capital to begin its work of helping countries rebuild after the destruction and disruption of WWII. The IBRD was also intended as a source of aid for developing countries.

Not all states agreed with the decisions taken at Bretton Woods. The USSR, Haiti, Liberia, and New Zealand all declared they would not be subject to the decisions taken at the conference.

The Bretton Woods Conference was followed by the Dumbarton Oakes Conference, held at Harvard University. Delegates from 39 states met, first from 21 August to 28 September 1944, and then, after the USSR delegation was replaced by one from China, in a second phase that ran from 29 September to 7 October. The conference set out in detail (12 chapters of text) just how the United Nations would be run. The organisation would take decisions via a combination of the Security Council (with executive powers) and the General Assembly of all member states. It was also decided to establish an International Court of Justice.

The promise that the USSR would participate in a future United Nations organisation was secured at the Yalta Conference of 4 to 11 February 1945, when Roosevelt, Churchill, and Stalin met once again. A reluctant Stalin was also persuaded to allow France a permanent seat on the UN's executive, the Security Council. A genuinely international organisation which included the world's most powerful players now seemed a realistic possibility. There were still plenty of doubters, though. Many more cynical diplomats and politicians remained convinced that powerful states would not give up part of their sovereignty to the UN, and world politics would, as it always had been, continue to be driven by the self-interest of certain powerful countries. Time would tell if this view was overly pessimistic or not.

The United Nations Organization (UNO) finally became a reality at the San Francisco Conference, more formally known as the United Nations Conference, which ran from 25 April to 26 June 1945. President Roosevelt had died on 12 April, and there was some doubt as to whether the conference would go ahead. Roosevelt's vice president, Harry S. Truman (1884 to 1972), became the new president. Truman gave the green light for the conference to go ahead, explaining later: "I said that it was what Roosevelt had wanted, and it had to take place if we were going to keep the peace. And that's the first decision I made as President of the United States" (Moskin, 9). Truman's speech opened the conference, and in it he emphatically stated: "We can no longer permit any nation, or group of nations, to attempt to settle their arguments with bombs and bayonets" (Moskin, 146).

50 countries participated in San Francisco and signed the United Nations Security Charter on 26 June, which established, according to the principles laid out at the Dumbarton Oakes Conference, the UN Security Council with its five permanent members: US, USSR, UK, China, and France, each with a right of veto. Initially, the USSR had wanted the veto right to include rejection of even discussing an issue at all, but this stance was softened to a veto once an issue was debated by the Security Council. Six other members would join the council on a rotation basis. Smaller states were not best pleased with the veto right of the Big Five, but without it, it is highly likely that neither the US nor USSR would have joined the UN at all. All signatories could send a five-person delegation to the General Assembly, and all members had a single vote there.

Unlike with the League of Nations, the United States Senate ratified the UN Charter by 89 votes to two. Truman commented that "The action of the Senate substantially advances the cause of world peace" (Moskin, 234). There were still some issues to thrash out, most significantly the inclusion of pro-fascist Argentina as a member but the exclusion of pro-Communist Poland (although they would sign the charter four months later).

The United Nations was officially put into operation on 24 October 1945, with its headquarters established in New York. The first meeting of the UN General Assembly was then held on 10 January 1946, and two weeks later, its first resolution was made: to ensure the peaceful use of atomic energy and the elimination of atomic weapons. On 17 January, the Security Council had its first meeting. The League of Nations was formally terminated in April that year, and its treaties and assets were passed on to the UN.

The United Nations, today expanded to 193 member states, continues to function as a body promoting the four aims set out in its charter: to maintain international peace and security, to develop friendly relations between nations, to promote cooperation to solve international problems and respect human rights, and to ensure the UN is a harmonising focal point between all nations in order to achieve its aims. October 24 is celebrated worldwide as United Nations Day.